But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus Christ, his Son, cleanses us from all sin.
The second reason why he wrote this epistle is in chapter 2, verse 1 John 1:1 . "These things write we unto you, that ye sin not." And so, the purpose of this epistle is to bring to you a life of victory over sin, to give you power over sin.