9 The first stage of liberty is to be free from crimes. Give heed, my brethren, give heed, that I may not by any means mislead your understanding as to the nature of that liberty at present, and what it will be. Sift any one soever of the highest integrity in this life, and however worthy he may already be of the name of upright, yet is he not without sin. Listen to Saint John himself, the author of the Gospel before us, when he says in his epistle, “If we say that we have no sin, we deceive ourselves, and the truth is not in us.” He alone could say this who was “free among the dead:” of Him only could it be said, who knew no sin.
It could be said only of Him, for He also “was in all points tempted like as we are, yet without sin.” He alone could say, “Behold, the prince of this world comes, and shall find nothing in me.” Sift any one else, who is accounted righteous, yet is he not in all respects without sin; not even such as was Job, to whom the Lord bore such testimony, that the devil was filled with envy, and demanded that he should be tempted, and was himself defeated in the temptation, to the end that Job might be proved. And he was proved for this reason, not that the certainty of his carrying off the conqueror's wreath was unknown to God, but that he might become known as an object of imitation to others.
And what says Job himself? “For who is clean? Not even the infant whose life is but a day's span upon the earth.” But it is plain that many are called righteous without opposition, because the term is understood as meaning, free from crime; for in human affairs there is no just ground of complaint attaching to those who are free from criminal conduct. But crime is grievous sin, deserving in the highest measure to be denounced and condemned. Not, however, that God condemns certain sins, and justifies and praises certain others.
He approves of none. He hates them all. As the physician dislikes the ailment of the ailing, and works by his healing measures to get the ailment removed and the ailing relieved; so God by his grace works in us, that sin may be consumed, and man made free. But when, you will be saying, is it consumed? If it is lessened, why is it not consumed? That is growing less in the life of those who are advancing onwards, which is consumed in the life of those who have attained to perfection.
Source: Tractates on the Gospel of John (New Advent)