I don't think it's worth wasting my time when there are already plenty of essays online that can say what I think better than I can.
Then please don't waste my time by posting in the first place.
The filioque did matter to our Fathers which is why they anathematized it at least two councils: the 8th Ecumenical Council in 879, and the Council of Blacharnae in 1285.
This was for Rome adding the filioque unilaterally, rather than introducing it before a council. The theology itself is supported, or at least hinted, by the fathers.
"I believe the Spirit to proceed from no other source than from the Father through the Son." Tertullian, Against Praxeas, 4:1 (A.D. 216).
"Now the Spirit indeed is third from God and the Son; just as the fruit of the tree is third from the root, or as the stream out of the river is third from the fountain, or as the apex of the ray is third from the sun." Tertullian, Against Praxeas, 8:1 (A.D. 216).
"We consider therefore that there are three hypostases, the Father and the Son and the Holy Spirit; and at the same time we believe nothing to be uncreated but the Father. We therefore, as the more pious and the truer course, admit that all things were made by the Logos, and that the Holy Spirit is the most excellent and the first in order of all that was made by the Father through Christ." Origen, Commentary on John, 2:6 (A.D. 229).
"Therefore the Spirit is said to receive from Christ, and Christ Himself from the Father." Marius Victorinus, Against Arium, I:12 (c. A.D. 355).
"Concerning the Holy Spirit I ought not to be silent, and yet I have no need to speak; still, for the sake of those who are in ignorance, I cannot refrain. There is no need to speak, because we are bound to confess Him, proceeding, as He does, from Father and Son." Hilary of Poitiers, On the Trinity, 2:29 (A.D. 357).
"For the present I forbear to expose their license of speculation, some of them holding that the Paraclete Spirit comes from the Father or from the Son. For our Lord has not left this in uncertainty, for after these same words He spoke thus,-- 'I have yet many things to say unto you, but ye cannot bear them now. When He, the Spirit of truth, is come, He shall guide you into all truth: for He shall not speak from Himself: but what things soever He shall hear, these shall He speak; and He shall declare unto you the things that are to come. He shall glorify Me: for He shall receive of Mine and stroll declare it unto you. All things whatsoever the Father hath are Mine: therefore said I, He shall receive of Mine and shall declare it unto you' (John 16:12-15). Accordingly He receives from the Son, Who is both sent by Him, and proceeds from the Father. Now I ask whether to receive from the Son is the same thing as to proceed from the Father. But if one believes that there is a difference between receiving from the Son and proceeding from the Father, surely to receive from the Son and to receive from the Father will be regarded as one and the same thing." Hilary of Poitiers, On the Trinity, 8:20 (A.D. 357).
"But I cannot describe Him, Whose pleas for me I cannot describe. As in the revelation that Thy Only-begotten was born of Thee before times eternal, when we cease to struggle with ambiguities of language and difficulties of thought, the one certainty of His birth remains; so I hold fast in my consciousness the truth that Thy Holy Spirit is from Thee and through Him, although I cannot by my intellect comprehend it. For in Thy spiritual things I am dull, as Thy Only-begotten says, Marvel not that I said unto thee, ye must be barn anew. The Spirit breathes where it will, and thou hearest the voice of it; but dost not know whence it comes or whither it goes. So is every one who is barn of water and of the Holy Spirit. Though I hold a belief in my regeneration, I hold it in ignorance; I possess the reality, though I comprehend it not." Hilary of Poitiers, On the Trinity, 12:56 (A.D. 357).
"For as the Son, who is in the Father and the Father in him, is not a creature but pertains to the essence of the Father (for this you also profess to say); so also it is not lawful to rank with the creatures the Spirit who is in the Son, and the Son in him." Athanasius, To Serapion, I:21 (A.D. 360).
"For He, as as been said, gives to the Spirit, and whatever the Spirit hath, He hath from the Word." Athanasius, Against the Arians, III:24 (A.D. 362).
"Even if the Holy Spirit is third in diginity and order, why need he be third also in nature? For that he is second to the Son, having his being from him and receiving from him and announcing to us and being completely dependent on him, pious tradition recounts; but that his nature is third we are not taught by the Saints nor can we conclude logically from what has been said." Basil, Against Eunomius, 3, PG 29:653B (A.D. 365).
"[A]lthough the Holy Spirit is behind the Son in dignity, yet not in nature. We have received that he is numbered third from the Father, the Lord saying in the tradition of baptism....But that he is thrust out to some third nature we have neither learnt nor ever heard." Basil, Homilies, Against Eunomius, PG 29:657D-660A (A.D. 365).
"The Holy Spirit ... is ever with the Father and the Son, and is from God, proceeding from the Father and receiving of the Son." Epiphanius, The Man Well-Anchore, 7 (A.D. 374).
"The Spirit is God, from the Father and the Son." Epiphanius, The Man Well-Anchored, 9 (A.D. 374).
"[N]either does any know the Spirit but the Father and the Son, the Persons from whom he proceeds and from whom He receives." Epiphanius, The Man Well-Anchored, 11 (A.D. 374).
"God ...is Life, the Son Life from Life, and the Holy Spirit flows from both; the Father is Light, the Son is Light, the Holy Spirit the third from Father and Son." Epiphanius, The Man Well-Anchored, 70 (A.D. 374).
"The Father always existed and the Son always existed, and the Spirit breathes forth from the Father and the Son..." Epiphanius, The Man Well-Anchored, 75 (A.D. 374).
"One, moreover, is the Holy Spirit, and we speak of Him singly, conjoined as He is to the one Father through the one Son, and through Himself completing the adorable and blessed Trinity." Basil, On the Holy Spirit, 18:45 (A.D. 375).
"One, moreover, is the Holy Spirit and we speak of Him singly, conjoined as He is through Himself completing the adorable and blessed Trinity." Basil, On the Holy Spirit, 18:45 (A.D. 375).
"Thus the way of the knowledge of God lies from One Spirit through the One Son to the One Father, and conversely the natural Goodness and the inherent Holiness and the royal Dignity extend from the Father through the Only-begotten to the Spirit. Thus there is both acknowledgment of the hypostases and the true dogma of the Monarchy is not lost." Basil, On the Holy Spirit, 18:47 (A.D. 375).
"If, however, any one cavils at our argument, on the ground that by not admitting the difference of nature it leads to a mixture and confusion of the Persons, we shall make to such a charge this answer;--that while we confess the invariable character of the nature, we do not deny the difference in respect of cause, and that which is caused, by which alone we apprehend that one Person is distinguished from another;-by our belief, that is, that one is the Cause, and another is of the Cause; and again in that which is of the Cause we recognize another distinction. For one is directly from the first Cause, and another by that which is directly from the first Cause; so that the attribute of being Only-begotten abides without doubt in the Son, and the interposition of the Son, while it guards His attribute of being Only-begotten, does not shut out the Spirit from His relation by way of nature to the Father." Gregory of Nyssa, To Ablabius-There are not three gods (A.D. 375).
"[T]he Holy Spirit is neither begotten or created ... but of the same substance with the Father and the Son." Epiphanius, Panarion, 74 (A.D. 377).
"But if there is really no hindrance to the third torch being fire, though it has been kindled from a previous flame, what is the philosophy of these men, who profanely think that they can slight the dignity of the Holy Spirit because He is named by the Divine lips after the Father and the Son?" Gregory of Nyssa, Against Macedonians, 6 (A.D. 377).
"For neither did the Universal God make the universe 'through the Son,' as needing any help, nor does the Only-begotten God work all things 'by the Holy Spirit,' as having a power that comes short of His design; but the fountain of power is the Father, and the power of the Father is the Son, and the spirit of that power is the Holy Spirit." Gregory of Nyssa, Against Macedonians, 13 (A.D. 377).
"One Father, one Son, one Holy Spirit must be confessed according to the divine tradition. Not two Fathers, nor two Sons, since the Spirit neither is the Son nor is called. For we do not receive anything from the Spirit in the same way as the Spirit from the Son; but we receive him (the Spirit) coming to us and sanctifying us, the communication of divinity, the pledge of eternal inheritance, and the first fruits of the eternal good." Basil, Homilies, PG 31:1433 (ante A.D. 379).
"If ever there was a time when the Father was not, then there was a time when the Son was not. If ever there was a time when the Son was not, then there was a time when the Spirit was not." Gregory of Nazianen, 5th Oration (31), 3 (A.D. 380).
"Our Lord teaches that the being of the Spirit is derived not from the Spirit Himself, but from the Father and the Son; He goes forth from the Son, proceeding from the Truth; He has no subsistence but that which is given Him by the Son." Didymus the Blind of Alexandria, The Holy Spirit, 37 (ante A.D. 381).
"Our Lord teaches that the being of the Spirit is derived not from the Spirit Himself, but from the Father and the Son; He goes forth from the Son, proceeding from the Truth; He has no subsistence but that which is given Him by the Son." Didymus the Blind, The Holy Spirit, 37 (ante A.D. 381).
"The Holy Spirit also, when He proceeds from the Father and the Son, is not separated from the Father nor separated from the Son. For how could He be separated from the Father Who is the Spirit of His mouth? Which is certainly both a proof of His eternity, and expresses the Unity of this Godhead." Ambrose, The Holy Spirit, 1:11:120 (A.D. 381).
"Learn now that as the Father is the Fount of Life, so, too, many have stated that the Son is signified as the Fount of Life; so that, he says, with Thee, Almighty God, Thy Son is the Fount of Life. That is the Fount of the Holy Spirit, for the Spirit is Life, as the Lord says: 'The words which I speak unto you are Spirit and Life,' for where the Spirit is, there also is Life; and where Life is, is also the Holy Spirit." Ambrose, The Holy Spirit, 1:15:172 (A.D. 381).
"For as the Son is bound to the Father, and, while deriving existence from Him, is not substantially after Him, so again the Holy Spirit is in touch with the Only-begotten, Who is conceived of as before the Spirit's subsistence only in the theoretical light of a cause. Extensions in time find no admittance in the Eternal Life; so that, when we have removed the thought of cause, the Holy Trinity in no single way exhibits discord with itself; and to It is glory due." Gregory of Nyssa, Against Eunomius, 1:42 (A.D. 384).
"The Holy Spirit is from the Father and the Son, not made nor created, nor begotten, but proceeding." Athanasian Creed (A.D. 400).
"As, therefore, the Father begat, the Son is begotten; so the Father sent, the Son was sent. But in like manner as He who begat and He who was begotten, so both He who sent and He who was sent, are one, since the Father and the Son are one. So also the Holy Spirit is one with them, since these three are one. For as to be born, in respect to the Son, means to be from the Father; so to be sent, in respect to the Son, means to be known to be from the Father. And as to be the gift of God in respect to the Holy Spirit, means to proceed from the Father; so to be sent, is to be known to proceed from the Father. Neither can we say that the Holy Spirit does not also proceed from the Son, for the same Spirit is not without reason said to be the Spirit both of the Father and of the Son. Nor do I see what else He intended to signify, when He breathed on the face of the disciples, and said, 'Receive ye the Holy Ghost.' For that bodily breathing, proceeding from the body with the feeling of bodily touching, was not the substance of the Holy Spirit, but a declaration by a fitting sign, that the Holy Spirit proceeds not only from the Father, but also from the Son." Augustine, On the Trinity, IV:20,29 (A.D. 408).
"If, therefore, that also which is given has him for a beginning by whom it is given, since it has received from no other source that which proceeds from him; it must be admitted that the Father and the Son are a Beginning of the Holy Spirit, not two Beginnings; but as the Father and Son are one God, and one Creator, and one Lord relatively to the creature, so are they one Beginning relatively to the Holy Spirit. But the Father, the Son, and the Holy Spirit is one Beginning in respect to the creature, as also one Creator and one God." Augustine, On the Trinity, V:14,15 (A.D. 408).
"And the Holy Spirit, according to the Holy Scriptures, is neither of the Father alone, nor of the Son alone, but of both." Augustine, On the Trinity, ,XV:17,27 (A.D. 408).
"And yet it is not to no purpose that in this Trinity the Son and none other is called the Word of God, and the Holy Spirit and none other the Gift of God, and God the Father alone is He from whom the Word is born, and from whom the Holy Spirit principally proceeds. And therefore I have added the word principally, because we find that the Holy Spirit proceeds from the Son also. But the Father gave Him this too, not as to one already existing, and not yet having it; but whatever He gave to the only-begotten Word, He gave by begetting Him. Therefore He so begat Him as that the common Gift should proceed from Him also, and the Holy Spirit should be the Spirit of both." Augustine, On the Trinity, XV:17,29 (A.D. 408).
"Wherefore let him who can understand the generation of the Son from the Father without time, understand also the procession of the Holy Spirit from both without time. And let him who can understand, in that which the Son says, 'As the Father hath life in Himself, so hath He given to the Son to have life in Himself,' not that the Father gave life to the Son already existing without life, but that He so begat Him apart from time, that the life which the Father gave to the Son by begetting Him is co-eternal with the life of the Father who gave it: let him, I say, understand, that as the Father has in Himself that the Holy Spirit should proceed from Him, so has He given to the Son that the same Holy Spirit should proceed from Him, and be both apart from time: and that the Holy Spirit is so said to proceed from the Father as that it be understood that His proceeding also from the Son, is a property derived by the Son from the Father. For if the Son has of the Father whatever He has, then certainly He has of the Father, that the Holy Spirit proceeds also from Him…Therefore the Spirit of both is not begotten of both, but proceeds from both."
Augustine, On the Trinity, XV:26,47 (A.D. 408).
"Some one may here inquire whether the Holy Spirit proceedeth also from the Son. For the Son is Son of the Father alone, and the Father is Father of the Son alone; but the Holy Spirit is not the Spirit of one of them, but of both.... If, then, the Holy Spirit proceedeth both from the Father and from the Son, why said the Son, 'He proceedeth from the Father'? Why, do you think, but just because it is to Him He is wont to attribute even that which is His own, of whom He Himself also is? Hence we have Him saying, 'My doctrine is not mine, but His that sent me.' If, therefore, in such a passage we are to understand that as His doctrine, which nevertheless He declared not to be His own, but the Father's, how much more in that other passage are we to understand the Holy Spirit as proceeding from Himself, where His words, 'He proceedeth from the Father,' were uttered so as not to imply, He proceedeth not from me? But from Him, of whom the Son has it that He is God (for He is God of God), He certainly has it that from Him also the Holy Spirit proceedeth: and in this way the Holy Spirit has it of the Father Himself, that He should also proceed from the Son, even as He proceedeth from the Father." Augustine, Homilies on John, 99:6,8 (A.D. 416).
"Since the Holy Spirit when he is in us effects our being conformed to God, and He actually proceeds from Father and Son, it is abundantly clear that He is of the divine essence, in it in essence and proceeding from it." Cyril of Alexandria, Treasury of the Holy Trinity, Thesis 34 (A.D. 425).
"Inasmuch as the Son is God and is by nature from God, the Spirit is His own, and is both in Him and from Him." Cyril of Alexandria, In Joel, 2:28 (A.D. 427).
"Call the Father the author, because the Son is from him, though he is not from the Son and because the Holy Spirit proceeds from him and from the Son. By giving birth to the Son, he gave it to him that the Holy Spirit proceeds from him as well." Augustine, Against Maximinus, 2:5 (A.D. 428).
“The Son comes from the Father; the Holy Spirit comes from the Father. The former is born; the latter proceeds. Hence, the former is the Son of the Father from whom he is born, but the latter is the Spirit of both because he proceeds from both. When the Son spoke of the Spirit, he said, 'He proceeds from the Father (Jn 15:26)', because the Father is the author of his procession. The Father begot a Son and, by begetting him, gave it to him that the Holy Spirit proceeds from him as well. If he did not proceed from him, he would not say to his disciples, 'Receive the Holy Spirit (Jn 20:22)', and give the Spirit by breathing on them. He signified that the Holy Spirit also proceeeds from him and showed outwardly by blowing what he was giving inwardly by breathing. If he were born, he would be born not from the Father alone or from the Son alone, but from both of them; he would beyond any doubt be the son of both of them. But because he is in no sense the son of both of them, it was necessary that he not be born from both. He is, therefore, the Spirit of both, by proceeding from both." Augustine, Against Maximinus, 2:14 (A.D. 428).
"He is the Spirit both of the Father and of the Son, seeing that He is poured forth in a way of essence from Both or in other words, from the Father through the Son." Cyril of Alexandria, Worship and Adoration, 1 (A.D. 429).
"For he [the Holy Spirit] is called the Spirit of Truth, and Christ is the Truth, and he is poured forth from him [the Son] just as he is also from God the Father." Cyril of Alexandria, To Nestorius, Epistle 17 (A.D. 430).
"Believe most firmly, and never doubt, that the same Holy Spirit, the One Spirit of the Father and the Son, proceeds from the Father and the Son. That He proceeds also from the Son is supported by the teaching both of Prophets and Apostles." Fulgence of Ruspe (North Africa), Rule of Faith, 11 (A.D. 447).
"The Spirit is also the Paraclete, who is himself neither the Father and the Son, but proceeding from from the Father and the Son. Therefore the Father is unbegotten, the Son is begotten, the Paraclete is not begotten, but proceeding from the Father and the Son." Council of Toledo II (A.D. 447).
"And so under the first head is shown what unholy views they hold about the Divine Trinity: they affirm that the person of the Father, the Son, and the Holy Ghost is one and the same, as if the same God were named now Father, now Son, and now Holy Ghost: and as if He who begot were not one, He who was begotten, another, and He who proceeded from both, yet another; but an undivided unity must be understood, spoken of under three names, indeed, but not consisting of three persons." Pope Leo the Great [regn. A.D. 440-461], To Turribius, Epistle 15 (A.D. 447).
"The Holy Spirit is neither generate nor ingenerate, but rather is He who proceeds from the Father and the Son, as a harmony, we may say of Both." Eucherius of Lyons, Spic. Rom., 5:93 (ante A.D. 454).
"And while in the property of each Person the Father is one, the Son is another, and the Holy Ghost is another, yet the Godhead is not distinct and different; for whilst the Son is the Only begotten of the Father, the Holy Spirit is the Spirit of the Father and the Son, not in the way that every creature is the creature of the Father and the Son, but as living and having power with Both, and eternally subsisting of That Which is the Father and the Son." Pope Leo the Great [regn. A.D. 440-461], Sermon 75 (ante A.D. 461).
"We believe that there is One God, Father, Son, and Holy Spirit; Father, in that He has a Son; Son, in that He has a Father; Holy Spirit, in that He proceeds from the Father and the Son (ex patre et filio)." Gennadius of Marseilles, De eccl. dogm., PL 58,980 (ante A.D. 495).
"[T]he faithful committed to our charge ought to be taught concerning the Holy Spirit that He proceeds from the Father and the Son, and therefore cannot be said to be either generate or ingenerate." Julianus Pomerius of Arles, The Contemplative Life, PL 59,432 (ante A.D. 498).
"The Spirit is said to be sent by the Father and the Son, and to proceed from Their substance... If you ask what distinction is to be drawn between generation and procession, there is clearly this difference, that the Son is begotten of One, but the Spirit proceeds from Both." Paschasius a Deacon of Rome, The Holy Spirit, 1:12 (ante A.D. 512).
"The Father is begotten of none, the Holy Spirit proceeds from the Father and the Son." Fulgence of Ruspe (North Africa), The Trinity, 2 (ante A.D. 517).
"Great and incomprehensible is the mystery of the Trinity. God the Father, God the Son, God the Holy Ghost, an undivided Trinity, and yet it is known because it is characteristic of the Father to generate the Son, characteristic of the Son of God to be born of the Father equal to the Father, characteristic of the Spirit to proceed from Father and Son in one substance of deity." Pope Hormisdas [regn. A.D. 514-523], Profession of Faith, PL 63:514B (A.D. 517).
"We for our part affirm that the Holy Spirit proceeds from the Father and the Son...it is the property of the Holy Spirit to proceed from the Father and the Son." Avitus of Vienne, Against King Gundobad (ante A.D. 523).
"The Holy Spirit is wholly the Father's and wholly the Son's, because He is by nature the one Spirit of the Father and the Son; for which cause He proceeds wholly from the Father and the Son; for He so abides as to proceed, and so proceeds as to abide." Fulgence of Ruspe (North Africa), To Ferrandus, Epistle 14 (ante A.D. 527).
We further declare that we hold fast to the decrees of the four Councils, and in every way follow the holy Fathers, Athanasius, Hilary, Basil, Gregory the Theologian, Gregory of Nyssa, Ambrose, Theophilus, John (Chrysostom) of Constantinople, Cyril, Augustine, Proclus, Leo and their writings on the true faith." Ecumenical Council of Constantinople II, Session I (A.D. 553).
"[T]he Father is unbegotten, the Son begotten, and the Holy Spirit proceeding from the Father and the Son." Cassiodorius, Expositio Psalmorum,Praef. 17 (ante A.D. 570).
"The Spirit proceeds essentially from the Son...the Redeemer imparted to the hearts of His disciples the Spirit who proceeds from Himself." Pope Gregory the Great (the Theologian) [regn. A.D.590-604], Moral Teachings drawn from Job, 1:22,2:92 (A.D. 595).
"Our Lord ... shews how the Spirit of Both so proceeds as to be coeternal with Both...He who is produced by procession is not posterior in time to those by whom He is put forth." Pope Gregory the Great (the Theologian) [regn. A.D.590-604], Moral Teachings drawn from Job, 25:4 (A.D. 595).
As I said before, it was an ad hoc reason for schism.
Any bishop that would enter communion with Rome would automatically cease to be an Orthodox bishop, unless Rome first repented of its heresies which have been condemned by numerous Councils
You are correct. We might, however, need to reasses what Roman doctrines are actually heresies, just as our Church has done and is doing for the non-Chalcedonians. That would take a spirit of love and charity. We are not required to believe their post-schism doctrine to share communion.
Since you are a parish priest, rather than a church historian, I can forgive you for being intellectually lazy. Please, however, don't try to teach me.