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.
1:9 confess our sins. To “confess” one’s sins does not mean merely to confess one’s sins in general, but rather to identify them specifically, and then to agree with God as to their specific sinful character, thus in reality repenting (that is, changing one’s mind) about them and viewing them as God does. Since Christ’s blood has already been shed to cover them, He is faithful to His Word and provides forgiveness in perfect justice.
1:9 cleanse us. The “confession” of this verse is not merely a pat formula that one can glibly apply and then all is well. When God forgives our sins, He also expects to “cleanse us from all unrighteousness” (not just from the penalty of unrighteousness). The Greek word for “cleanse” is katherizo (from which we get our English word “catharsis”) and is often translated “purify” and even “purge.”