1:8 deceive ourselves. The heresy of “perfectionism”—that is, the claim that our sin-nature has been completely eradicated, so that we no longer commit sin—is self-deception. It is related to the Gnostic heresy of the time which claimed that the soul had been set free from one’s sinful flesh.
1:10 have not sinned. To say either that we “have no sin” (I John 1:8) or “have not sinned” (I John 1:10) is presumptuous, blasphemous and false. Those who make such claims may deceive themselves, but others can easily discern sin in them.