John Calvin Commentary 1 John 1:8

"If we say that we have no sin, we deceive ourselves, and the truth is not in us." — 1 John 1:8 (ASV)

If we say. He now highlights grace because it is necessary; for since no one is free from sin, he implies that we are all lost and ruined, unless the Lord comes to our aid with the remedy of pardon. The reason he emphasizes so much that no one is innocent is so that all may now fully know that they need mercy to deliver them from punishment, and that they may thus be more stirred to seek the necessary blessing.

The word sin here means not only corrupt and vicious inclination, but the fault or sinful act which truly makes us guilty before God. Besides, since it is a universal declaration, it follows that none of the saints—those who exist now, have existed, or will exist—are exempt from this. Therefore, Augustine most fittingly refuted the objection of the Pelagians by citing this passage against them; and he wisely thought that the confession of guilt is required not for the sake of humility, but so that we do not, by lying, deceive ourselves.

When he adds, and the truth is not in us, he confirms the previous sentence, as is his custom, by restating it in other words; although it is not a simple repetition (as in other places), rather, he says that those who boast in falsehood are deceived.