Sin certainly is a significant theme in Flannery O'Connor's Wise Blood. The theme of sin is especially illustrated through examples of moral corruption. All of the characters are morally corrupt in their own way, even those who think, or at least preach, that they have been redeemed.
O'Connor especially uses Hazel Motes to illustrate the theme of sin or moral corruption. One example can be seen with respect to Motes's decision to try and seduce Sabbath, the daughter of the blind street evangelist Asa Hawks. His decision to try and seduce her is based purely on his personal desire to prove that the whole idea of both sin and redemption are completely superfluous. We see Motes's lack of faith in the existence of sin and redemption early on in the book, but especially when he begins preaching from his Essex, like when he tries to preach to movie-goers as they enter the cinema:
I'm going to preach there was no Fall because there was nothing to fall from and no Redemption because there was no Fall and no Redemption because there was no Fall and no Judgement because there wasn't the first two. Nothing matters but that Jesus was a liar. (101)
A second example is seen when Motes murders the actor who looks exactly like him that Onnie Jay Holy hires to play a preacher for the competing church Holy established, the Holy Church of Christ Without Christ. Motes murders the actor by repeatedly driving over him with the Essex he preaches his sermons from.
Even the street evangelist Asa Hawks is guilty of sin in the form of pretending to be blind as a means of getting more followers and thereby more money. He had told his followers that he would blind himself out of faith that Christ would heal him; however, he lost both his nerve and enough faith to do so and scarred his eyes but did not truly blind them.