Charles Spurgeon Commentary 1 John 3:5-6

"And ye know that he was manifested to take away sins; and in him is no sin. Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither knoweth him." — 1 John 3:5-6 (ASV)

And ye know that he was manifested to take away our sins; and in him is no sin. Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.

That is to say, if sin is the habitual course of our life, we do not truly know the Lord. He who walks with God endeavors with all his might to be free from sin, and he is sanctified by abiding in Christ.