In your tradition, by what means does the blood of Christ "wash away the filth of our transgressions"?
The scriptures refer to the giving of his life, or the shedding of his blood, as a ransom, as washing or cleansing, as the establishment of the covenant - the full, sufficient, eternal price paid to secure the remission of all our sins. Nothing needs to be added to the value of the price he paid. The forgiveness it purchased is received freely, as a gift, to the repentant but believing sinner.
You see how the wording of your liturgy at least appears to say something different. But does it? This is what I desire to understand.
What you appear to be saying is that the washing away of the filth of one's transgressions is a one-time thing. One day we are sinful transgressors, the next we make a decision to believe in Christ and somehow His blood on the Cross 2000 years ago instantly wipes our slate clean for all time. While we might sin again, it's not going to affect our salvation; so our continued repentance is rather superfluous. Therefore, salvation for the individual in your tradition is accomplished by a one-time intellectual decision and no real effort of continued repentance on their part. This does seem familiar from what I remember of my Evangelical experience; though there are variances. Forgive me if I have this wrong in your case, but this is the kind of thinking I have witnessed amongst Evangelicals. And while the claim is that as long as one continues to "believe in Jesus" one is saved and "made perfect in Christ", in reality the affects are quite at odds with this and I have seen this lack of repentance produce the most horribly moralistic set of rules that one must abide by to be accepted in the group. This develops judgemental attutudes of the "saints" towards "sinners". Because the "sinners" don't quite manage to follow the prescribed rules of conduct of the group they are considered almost unsavable or backsliders. These people are ultimately made to feel acutely ostracised and cast out.
Quoting from a book I'm reading at the moment, the difference with Orthodoxy is this... The Church embraces all people with all their problems and worries, and strives to transfigure them. The Church, in any case, is a spiritual Hospital which heals people's illness. She does not reject anyone. Only groups of anthropocentric political, social and even religious systems reject peopel who are not able, or who do not want to be fully obedient to their principles. In all these systems there is an intense mysticism; an ideology dominates which demands obedience to abstract commandments. And for this reasons we cannot speak of obedience but discipline. Furthermore, a mania for perfection dominates. They want you to be perfect according to the principles of the system. Alas, if you should sin consciously or unconsciously. They will cast you out and give the stigma of crossing you off to all the friends of the system. they will make the decision public, so that it becomes known and the system is not put to blame. And I believe that this mania for perfection is an indicative sign of an extistent schizophrenia. The person who has the mania to be perfect is in reality a schizophrenic. The Church, without supporting or justifying the sick person, receivwes him as he is, and strives, with the ways she has at her disposal, to cure him. this is why, in the Church there are people of various spiritual ages.
[The Illness and Cure of the Soul in the Orthodox Tradition, by Metropolitan of Nafpaktos Hierotheos.]
The Orthodox view of salvation is ontological not intellectual. We are joined sacramentally with Christ at baptism; old man dies, new man is born from above; water and spirit. However, this birth is not completed or finalised; we have merely entered the Hospital of the Soul, which is the Church to affect the healing of our various illnesses. Being flawed human beings we will relapse and continue to sin. Even if the sins are little they separate us from God. We have an expression that the pristine garment of our baptism is made filthy by our sins. Unless we repent of those sins, they will stain our relationship with God and our fellow man. For Lent we fast in repentance of all our sins, those we know of and those we are ignorant of. Our baptism garment is made clean again through the tears of our repentance. This is part of our salvific experience, part of our sanctification.
Just to put your quote from the Matins on Friday of the week before Lent in context;
“God has shown mercy to us. Let us in turn show mercy: let us feed the poor, and with the divine water of fasting, let us wash the defilement from our souls.” Then we say, “O heavenly angels, entreat the Giver of good to accept in His infinite mercy our poor and mean repentance.” Continued repentance might be a strange concept for one who believes that a one-time intellectual decision for Christ makes our salvation a done deal - if indeed that is what you believe. However, as Orthodox Christians we are always aware of the weakness of our hearts.
St James tells us that the faith that saves is the complete faith, not simply the intellect accepting and the tongue confessing, but the whole man or woman trusting in the Living God. Our faith is a life-time and beyond relationship with God. Justification for us is dynamic and alive and continuing. We believe that our faith grows and affects what we do or else it dies. While it might be your opinion that “Faith alone” saves, we don’t agree. A static faith, does not sanctify, it stagnates and dies; the danger being that the one who believes himself to be saved by that one-time declaration ignores the very sins that prevent him from acquiring the Holy Spirit. The living faith is one in which we nurture our faith in God and our love for Him through our responses to the needs of others and our repentance of our own sins.
St James shows us an example of a living and active faith by pointing to the faith of Abraham. When Abraham received the call to forsake all and follow God he did so with all that was to entail. This is all a crucial lesson for us in our understanding of justification by faith. Abraham’s sanctification and justification is not a momentary, intellectual, static, or one-time event. His faith is dynamic, a growth process which finds its realisation in good works and repentance. It is this living and active faith, St James declares, the faith which saves!
So yes, the gift of salvation is freely given by God yet we must do our part by taking take of what he offers to us. We are workers together with Him as St Paul calls it. This is synergy; this is cooperation with a living God in a living relationship.
Please don't think that I'm in any way "bashing" your tradition. I'm merely trying to answer your question to the best of my ability.