John Calvin Commentary 1 John 1:10

"If we say that we have not sinned, we make him a liar, and his word is not in us." — 1 John 1:10 (ASV)

We make him a liar. he goes even further: those who claim purity for themselves blaspheme God. For we see that He everywhere represents the whole human race as guilty of sin.

Whoever then tries to escape this charge wages war with God, and accuses Him of falsehood, as though He condemned the undeserving. To confirm this, he adds, and his word is not in us; as though he had said that we reject this great truth: that all are under guilt.

From this we learn that we make proper progress in the knowledge of the word of the Lord only when we become truly humbled, so as to groan under the burden of our sins, learn to flee to the mercy of God, and acquiesce in nothing else but His paternal favor.