If we say that we haven't sinned, we make him a liar, and his word is not in us.
"It would be difficult to find any single passage of Scripture more crucial and fundamental to daily Christian living than 1 John 1:5-10. For here, in a few brief verses, the ’disciple whom Jesus loved’ has laid down for us the basic principles which underlie a vital walk with God." [Note: Hodges, "Fellowship and . . .," p. 48.] 