After John giving some tests to see if you are really of the faith, he assures believers that even though they will still sin, the Advocate, Jesus Christ the Righteous, is always on our side proclaiming that He has taken the penalty sufficient for all.
1 John 2:1-2
1 My little children, I am writing these things to you so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous;
2 and He Himself is the propitiation for our sins; and not for ours only, but also for those of the whole world.