Saint Augustine (354-430AD) is one of the greatest Christian thinkers of all time. He fought the fight for the true understanding of justification against the heretic, Pelagius. If Pelagius would have won the justification controversy the Christian understanding would be that man's will is free to choose God and with right training one can become a Christian. Augustine argued that man's will is in bondage to sin because of the fall in Adam and in order for man to be converted to Christ, his heart would have to be changed by Christ.
Augustine understood what has come to be known as irresistible grace. Augustine as a young man hated God and he did all he could to run away from the need that God had placed on his heart. Augustine was attempting to run from his own sinful heart. This is seen in the following Confession. While meditating upon this section from his writings, any converted sinner has to see himself in these words. Do you see yourself?
And what is there in me that could be hidden from thee, Lord, to whose eyes the abysses of man's conscience are naked, even if I were unwilling to confess it to thee? In doing so I would only hide thee from myself, not myself from thee. But now that my groaning is witness to the fact that I am dissatisfied with myself, thou shinest forth and satisfiest.
Thou art beloved and desired; so that I blush for myself, and renounce myself and choose thee, for I can neither please thee nor myself except in thee. To thee, then, O Lord, I am laid bare, whatever I am, and I have already said with what profit I may confess to thee. I do not do it with words and sounds of the flesh but with the words of the soul, and with the sound of my thoughts, which thy ear knows. For when I am wicked, to confess to thee means nothing less than to be dissatisfied with myself; but when I am truly devout, it means nothing less than not to attribute my virtue to myself; because thou, O Lord, blessest the righteous, but first thou justifiest him while he is yet ungodly.
My confession therefore, O my God, is made unto thee silently in thy sight--and yet not silently. As far as sound is concerned, it is silent. But in strong affection it cries aloud. For neither do I give voice to something that sounds right to men, which thou hast not heard from me before, nor dost thou hear anything of the kind from me which thou didst not first say to me.
-Saint Augustine, Confessions, 10.2