If your interpretation of this scripture is correct, you are calling yourself a liar for you have transgressed the law many times just in postings on this board.
Do some research on the word "keepeth". The Greek "
tereo" is from the Greek word "theoreo" as is understood as to perservere in watching or guarding something. It does not denote in any way a sinless perfection. In fact John begins with.....
1Jo 2:1¶My little children, these things write I unto you, that ye sin not.
And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
A Christian guards the commandments of God with his heart(Not perfectly). A false brethern does not perservere in the commandments nor cares to guard them in their heart.
Perfection is not the doctrine. John even makes this clear throughout his letter, even from the very first sentence.