(the following is excerpted from pages 59-63 of The Teachings of the Holy Orthodox Church
by Rev.Michael Azkoul, edited by Hieromonk (now Bishop) Gregory; 1986 Dormition Skete Publications
)THE UNCREATED ENERGIES
The Uncreated Energies of God are the means by which the Three Persons of the Holy Trinity created the world and the way in which they ordinarily communicate with it - save the Incarnation which is the actual descent of the Person of God the Son into the world, "who was made flesh and dwelt among us" (John 1:14). The Uncreated Energies differ from both the essence and the Persons of the Trinity, albeit related to both. They are "movement" or "rush of God" out of His essence (St.John of Damascus) or "the rays of Divinity penetrating the created universe" (St.Dionysios the Areopagite). According to St.Basil the Great"The energies are numerous and the essence of God simple and what we know when we say God is in fact His energies. We do not presume to approach His essence. His energies come down to us, but His essence remains beyond our reach."
The energies belong to God's essence, and to use a common patristic simile, proceed from Him as rays from the sun. Here, too, there is no time sequence.
Furthermore, although God the Father created all things through the Son and in the Holy Spirit, they acted by the energies of their common essence. "The energies of the uncreated essence," writes St.Cyril of Alexandria, "is a common action while, at the same time, those energies belong and is a contribution of each Person in a special way."  In other words, the divine energies are the means by which the Trinity creates and communicates inasmuch as the divine essence is forever "immoble" and "incommunicable."
Thus, in reconciling the apparent contradiction between the words "no man has seen God at any time" and "Blessed are the pure in heart for they shall see God," St.Gregory of Nyssa says that "the Lord indeed speaks the truth when He promises that God will be seen by the pure of heart and St.Paul does not deceive us when he asserts that none have seen God at any time nor can see Him. For He is incomprehensible by nature, but falls within the range of our experience in His energies, that is, He may be contemplated in the things which point to Him." 
The energies are not the essence of the Trinity, but they express and are no less divine, coming forth from the essence through the divine Persons.
Of course, there have been and still are those who deny any distinction between essence and energy. St.Gregory Palamas replied to his contemporary adversaries that such a distinction is necessary to protect the integrity of both the Creator and the creation."If, according to the nonsense of Akindynos and those with him, the divine energy is nothing different from the divine essence, then, the act of creating - which is proper to the energy - will in no way differ from the acts of begetting and procession which is proper to the divine essence. But if to create in no way differs from begetting and procession, then created things differ in no way from Him Who is begotten and Him Who proceeds. And if, according to our adversaries, such is the case, then, neither the Son nor the Spirit differ from creatures, since all things are begotten and/or proceed from God the Father; thus, the creation will be deified and the divine Persons will be ranked with their own creatures. For this very reason the divine Cyril (of Alexandria), distinguishing between the essence and energy, says, 'The act of generation is proper to the divine nature whereas the act of creating belongs to His divine energy.' Then, stating the obvious, he adds, 'Nature and energy are not the same.'"
The only way to deflect St.Gregory's logic while, at the same time, denying any distinction between essence and energy in God is to declare the energies - grace and lights, etc. - to be created and to reassign the positive and moral qualities which belong to those energies - "mercy," "goodness," "love,"  "patience," etc. - to the divine Nature as "attributes." This is precisely what the theologians of the heterodox West did; but not without consequences.
First, with regard to grace, they could no longer safely speak of salvation as participation in the divine Nature (II Pet. 1:4). Otherwise, such participation in the divine Nature would, as it did in the case of so many medieval mystics, lead to pantheism. Second, grace in the official theology of the apostate West lost its cosmological character, having little to do with divine creating and limited almost exclusively to God's relationship with man. The Scholastics did not listen to St.Ambrose who said, "Divine grace reaches even to the life of the locust." 
The theological literature during the late Middle Ages and Reformation period show that grace was understood as a created power of God, His spontaneous, unmerited favor in the "regeneration," "sanctification" and "salvation" of sinners. The followers of Augustine, both Roman Catholic and Protestant, perceived grace to be compulsory and irresistable - inasmuch as our depraved human will would turn away from grace were it not forced on us. Some theologians connected grace with the Sacraments and some did not. They spoke of being "in the state of grace," but not that grace was a deifying process.
Also, the divine Light came to be conceived in the heterodox West as God Himself (lux divina), but distinguished from the light of nature (lux natura). The first they identified with "the light of glory," the "light of the Saints" and illumination for those in "the state of grace." The "light of nature" accounted for the spiritual and intellectual accomplishments of pagans and unbelievers. It was, in fact, the "divine Light" reflected in nature, in her laws, in the rationality and beauty of the cosmos. In modern times, "light" has come to stand for the "light" of reason - a new idea, clarity, vision.
In Orthodoxy, grace and light have more than a creative and providential purpose. They are manifested also to realize the Divine Plan - to sanctify and transfigure all that God has made. "God," says St.Maximos the Confessor, "has created us in order that we may become partakers of the Divine Nature, that we may enter into eternity, that we may resemble Him, that is, being deified by His Grace through which all things were made."  The Divine Light, too, has the purpose of uniting the creation with God; but more, it is a visitation from the future, from "the age to come" and is often called by the Fathers, "the light of the eigth Day." Light is usually associated with the Presence of the Holy Spirit, as St.Seraphim of Sarov and St.Symeon the New Theologian tell us.
More will be said about the soteriological  dimension of the Uncreated Energies in another chapter, but a few more words should be said about the Divine Light before we move on to the next subject.
Both Grace and Light describe the Divine Energies, not the Divine Essence. Therefore, as St.Gregory Palamas states, "God is Light not according to His Essence but according to His Energy."  If for no other reason, Light cannot be viewed as a metaphore and if God dwells in "unapproachable Light," as St.Paul exclaims (1 Tim. 6:16), He is basking in His Own Energies, even as the Lord on Mt.Tabor. St.Leo the Great, the Latin Father, speaks of the glory of the Kingdom of God as Light, which Christ made visible to the Apostles in His transfigured body. He also distinguished between the vision of the divine glory communicated by Christ and "the ineffable and inaccessible vision of Divinity itself,"  that is, between energy or operation and essence.
Moreover, the countless Scriptural references to Light - "God is Light" (I John 1:5); "I am the Light of the world" (John 8:12); "the righteous shall shine as the sun in the Kingdom of their FAther" (Matt. 13:43), etc. - cannot be understood as literal similies, for too many Saints have experienced the Light as the Presence of Divinity. Thus, St.Paul on his way to Damascus or St.Stephen the Protomartyr or St.Anthony the Great "in his battle for inner quiet" received now
the Light of the Kingdom, of "the age to come."  They received the Light of the Holy Spirit "shining in their hearts," St.Basil the Great testifies. 
This teaching about the Divine Light - and Grace - has a tradition which reaches beyond the Old Testament, to Eden itself where Adam basked in "the divine illumination and radiance" (St.Gregory Palamas). And later, we know that the face of Moses, when he came down from Mt.Sinai with the Ten Commandments, was glorious with the Light of God (Ex. 34:28). Everywhere in the Scriptures and Fathers one can find references to the Divine Light and, therefore, it is unfair to say, as some have, that this teaching is a "devleopment" of late Byzantine theology.Notes
51. On the Holy Trinity
, 6 PG 75 1056A.
52. On the Lord's Prayer
, Sermon 6.
53. Physical, Theological .... Chapters,
96 PG 150 1189B.
54. Lossky says that we ought to speak of a "love-energy" (The Mystical Theology
...., p.81), but Dr.Alexander Kalomiros may also be right that "love," for example, may be the way in which we experience the energy (See his "The River of Fire," in The Saint Nectarius Orthodox Conference
..., pp. 103-131)
XLIII PG 91 640BC.
57. Soteriological is the adjective of soteriology. See glossary.
58. Against Akindynos
PG 150 823A.
LI PL 54 310B.
60. St. Gregory Palamas Concerning the Holy Transfiguration
PG 151 428AB.
61. Against Eunomios
, PG 29 640AB; and St.Macarios of Egypt, Spiritual Homilies
V 8 PG 32 513B.