1 John 2:2-5

and he is the propitiation for our sins: and not for our's only, but also for the sins of the whole world. And hereby we do 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 is the love of God perfected: hereby know we that we are in him.