What the ...?

"And in him is no sin. 6 No one who lives in him keeps on sinning. No one who continues to sin has either seen him or known him . . . 9 No one who is born of God will continue to sin, because God's seed remains in him; he cannot go on sinning, because he has been born of God.

These words come from chapter 3 but if you look back to chapter 1 John states this.

"the blood of Jesus, his Son, purifies us from all sin. 8 If we claim to be without sin, we deceive ourselves and the truth is not in us. 9 If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness. 10 If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives."

My problem here is that these two statements appear contradictory and yet they are stated in same short letter. I remember you stating that there are no contradictions and this only means that we have to dig deeper (you quoted someone else with this statement, maybe Nygren?). I was curious if you had an explanation for what appears to be a blatant contradiction in John's letter.