In the next place, throwing a slur upon the exhortations spoken and written to those who have led wicked lives, and which invite them to repentance and reformation of heart, he asserts that we say “that it was to sinners that God has been sent.” Now this statement of his is much the same as if he were to find fault with certain persons for saying that on account of the sick who were living in a city, a physician had been sent them by a very benevolent monarch. God the Word was sent, indeed, as a physician to sinners, but as a teacher of divine mysteries to those who are already pure and who sin no more.
But Celsus, unable to see this distinction—for he had no desire to be animated with a love of truth—remarks, “Why was he not sent to those who were without sin? What evil is it not to have committed sin?” To which we reply, that if by those “who were without sin” he means those who sin no more, then our Saviour Jesus was sent even to such, but not as a physician. While if by those “who were without sin” he means such as have never at any time sinned—for he made no distinction in his statement—we reply that it is impossible for a man thus to be without sin.
And this we say, excepting, of course, the man understood to be in Christ Jesus, who “did no sin.” It is with a malicious intent, indeed, that Celsus says of us that we assert that “God will receive the unrighteousness man if he humble himself on account of his wickedness, but that He will not receive the righteous man, although he look up to Him, (adorned) with virtue from the beginning.” Now we assert that it is impossible for a man to look up to God (adorned) with virtue from the beginning.
For wickedness must necessarily first exist in men. As Paul also says, “When the commandment came, sin revived, and I died.” Moreover, we do not teach regarding the unrighteous man, that it is sufficient for him to humble himself on account of his wickedness in order to his being accepted by God, but that God will accept him if, after passing condemnation upon himself for his past conduct, he walk humbly on account of it, and in a becoming manner for the time to come.
Source: Against Celsus (New Advent)