1 John 2:2-6

and he is the propitiation for our sins; and not for ours only, but also for the whole world. And hereby we know that we know him, if we keep his commandments. He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him; but whoso keepeth his word, in him verily hath the love of God been perfected. Hereby we know that we are in him: he that saith he abideth in him ought himself also to walk even as he walked.