If we say that we haven't sinned, we make him a liar, and his word is not in us.
If we say that we have not sinned ... This is the most blatant and offensive of all the false theories.  "To go to the length of denying past sin and present guilt, is not only to becloud ourselves with sophistry but to give the lie to God himself."[41] God gave his only begotten Son upon the cross that man might be saved from sin, a salvation that was impossible for any man apart from God's redeeming act.  If man had not been sinful and utterly helpless to achieve salvation for himself, all of the heavenly outpouring of God's merciful visitation in the person of his Son was unnecessary; the crucifixion was a useless murder; and every promise of the gospel is essentially a lie.  John's language here is certainly not too strong.  People who deny their need of redemption from sin, through the pretense of not ever having sinned, are of all people most guilty and contemptible.  "To say that we have not sinned is not just to tell a deliberate lie, or to be self-deceived, but actually to accuse God of lying, to make him a liar."[42]