Think of this verse:
7But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
1 John 1:7
It seems from this verse that the blood of Jesus Christ has no power to cleanse us from our sin if we do not walk in the light.
Can an unconfessed sin be forgiven?
9If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
1 John 1:9
Gotta think about this. The Bible says a lot about
A) those sins we do that we don't realize is a sin.
B) those sins we do that we realize is a sin but which we don't confess.