How is a sinner transformed? What steps does the sinner take in order to be transformed?
I'm going to let Saint Theophan the Recluse answer that, quoting from
The Path to Salvation,
"The grace-filled Christian life is supposed to begin in baptism. But those who preserve this grace are rare; the majority of Christians lose it. We see some people who are more or less depraved in their present lives, because they had poor beginnings which were allowed to develop and take root in them. Others perhaps had good beginnings, but during the early years of their youth, whether by personal inclination or through temptation from others, forgot these beginnings and acquired evil habits. Such people no longer lead a true Christian life. Our holy faith offers the Mystery of Repentance for this.
We have an advocate with the Father, Jesus Christ the righteous (I Jn. 2:1). If you have sinned, acknowledge the sin and repent. God will forgive the sin and once again give you
a new heart...and a new spirit (Ez. 36:26). There is no other way: Either do not sin, or repent. Judging by the number of those who have fallen away from Baptism, one could even say that repentance has become for us the only source of true Christian life.
"It is necessary to know that in the Mystery of Repentance some merely have to be cleansed, and the gift of the grace-filled life, previously assimilated and operating within them, will be rekindled. For others, the beginning of this life has just been established within them, or it is being given and accepted anew. We will be examining the latter case.
"With regard to the second item we have mentioned, it is a decisive change for the better, a breaking of the will, a turning away from sin and a turning to God, or a kindling of the fire of zeal for exclusively God-pleasing things, with renunciation of the self and everything else. It is above all characterized by an extreme breaking of the will. If a person has acquired evil habits, he must now rend himself. If he has offended God, he must now grieve in the fire of just judgment. A repentant person experiences the pain of a woman giving birth, and, in the feelings of the heart, he encounters, as it were, the tortures of hell. To the lamenting Jeremiah, the Lord
commanded destroy and
build and plant (Jer. 1:10).
The lamenting spirit of repentance is sent by the Lord to the earth so that when it passes into those who accept it, to the dividing asunder of soul and spirit, and of the joints and marrow (Heb. 4:12), it destroys the old man and lays the foundation for the creation of the new. Within the repentant person there is first fear, then the lightness of hope; sorrow, then comfort; terror to the point of despair, then the breath of the consolation of mercy. One thing replaces another, and this supplies or keeps a person who is in a state of corruption or parting with life in the hope, however, of receiving new life.
"It is something painful, but it saves. It is therefore inevitable that whoever has not experienced such a painful break has not yet begun to live through repentance. It is impossible for a person to begin cleansing himself in everything without having gone through this crucible. Decisive and active resistance to sin comes only from hatred of it. Hatred of sin comes only from a sense of evil from it; the sense of evil from it is experienced in all its force in this painful break within repentance. Only here does a person sense with his whole heart what a great evil sin is; afterward he will run from it as he would from the fire of Gehenna. Without this painful experience, even if he begins cleansing himself in some other way, he will be able to cleanse himself only slightly, more outwardly than inwardly, more in actions than in disposition. That is why his heart will remain unclean, like unsmelted ore.
"Such change is brought about in the human heart by divine grace. This alone can inspire a man to raise his hand to himself and bring himself to God in sacrifice.
No man can come to Me, except the Father which hath sent me draw him (Jn. 6:44). God Himself gives a new heart and spirit (cf. Ez. 36:26). Man grieves for himself. Having been fused with flesh and sin, he became one with them. Only an outside, higher force can separate him and arm him against himself.
"Thus, grace produces change in the sinner, but this does not come about without free assent. In Baptism, grace is given to us at the moment the mystery is performed upon us; however, free will comes later and assimilates to itself what has been given. In repentance, then, free assent must participate in the very act of change.
"Change for the better and turning to God must seemingly be instantaneous or sudden, and so does it happen. In preparation, however, change undergoes several stages signifying the combining of freedom with grace, where grace gains mastery of the freedom and freedom is subordinated to grace. These stages are necessary for everyone. For some, the stages go by quickly, while for others, the process continues for many years. Who can keep track of everything that is going on here, especially when the ways of action of grace within us are so varied, and the conditions of people in whom they begin to act are infinite in number? It is necessary, however, to expect that, with all this variation, there is one general aspect of change that no one can escape. Every repenting man is a man who lives in sin, and every such man is recreated by grace. Therefore, it is on the basis of an understanding of the sinner's condition in general, and the basis of the relationship of freedom with grace that we are able to depict this process and characterize it through principles."
And he goes on quite a bit more on all this, very good book.