I knew that verse would appear sooner or later. Just like Romans 7 it is completely misused to argue in favour of continuing in sin.
The context of that verse is repentance.
1Jn 1:5 This then is the message which we have heard of him, and declare unto you, that
God is light, and in him is no darkness at all.
1Jn 1:6 If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth:
1Jn 1:7 But
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.
The blood will only cleanse someone if they are walking in the light as He is in the light. If 1Joh1:8-10 is evidence of indwelling sin then one cannot walk in the light as He is in the light and thus John is contradicting Himself.
The true context of 1Joh1:8 is that it is necessary to confess sin prior to being able to walk in the light as He is in the light. Confession comes before cleansing.
1Jn 1:8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
1Jn 1:9 If we confess our sins, he is faithful and just to forgive us our sins, and to
cleanse us from all unrighteousness.
1Jn 1:7 But 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.
All unrighteousness is sin and it must therefore be put off that one may walk in the light.
One cannot walk in the light unless they first confess and forsake their sin. The Prodigal Son in Luke 15 had to leave the pig pen and return to the father and then confess his sin. He was not cleansed while remaining in the pig pen.
If 1 Joh1:8-10 is teaching that the sin never stops in a Christian then John is contradicting himself for later he writes...
1Jn 3:8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
1Jn 3:9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
1Jn 3:10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
1Jn 5:18 We know that whosoever is born of God sinneth not; but he that is begotten of God keepeth himself, and that wicked one toucheth him not.
The truth is he is not contradicting himself because 1Joh 1:8-10 is clearly in the context of repentance.
Here is a link to an article I wrote where I address succinctly 1Joh1:8-10. Please take the time to read it.
http://standingthegap.org/If we say we have no sin.htm