Saint Theophan The Recluse-Rising to the Promise to Dedicate one's Life to God.

It would seem that everything is already done once one has resolved to abandon sin, and all that is left is the action. Precisely — one can act — but what kind of activity will this be, and what kind of spirit will it contain? The person is only left with himself so far. If he begins to act, beginning from this point, then he will be acting from himself and for himself, even though it be morally right. This will be an egotistical, pagan morality. There are people who say that they do good for goodness' sake — that is, they do it because human dignity requires it, or because it would be ignoble and imprudent to act any other way. 
All such people who act in this spirit retort that their education is internal, and the moral human being has not been completely formed — they have returned to themselves, but they have not turned from themselves to God and brought themselves as sacrifices to Him, which means they have stopped halfway. The goal of human freedom is not in freedom itself, nor is it in man, but in God. By giving man freedom God has yielded to man a piece of His divine authority, but with the intention that man himself would voluntarily bring it as a sacrifice to God, as a most perfect offering. Therefore, if you have mastered yourself, now give yourself to God. When you sinned, you not only lost yourself, but in losing yourself you took yourself away from God. Now, having returned from the captivity of sin, after you have mastered yourself, return yourself also to God.

It would also seem that turning away from yourself to God ought to be an easy and simple matter, like, for example, turning from west to east. But, after all, the sinner turning towards God is not an entity independent from Him, and he does not approach Him without anything trailing behind. No, like a runaway slave returning to his master, he appears as one guilty before the King and Judge. He needs to approach in such a way that he will be accepted. In human affairs a master accepts his slave, and the king has mercy on the guilty when each of them approaches admitting his guilt, repents of it and gives a sincere promise to be henceforth completely changed.

It is the same for a sinner returning to God. He will be accepted by God if he a) admits his sins, b) repents of them, and c) makes a vow not to sin. These are the necessary acts for ardent unification with God, upon which depends the steadfastness of the new life, perfection of it, and good hope for faithful action according to its demands. When the Prodigal Son returned to his father, he said: I will say, I have sinned — admitting the sin; I am not worthy — repenting; make me as one of thy hired servants — the promise to work (cf. Lk. 15:18,19).

Taken from "The Path to Salvation" By Saint Theophan the Recluse