This is how we know that we know him: if we keep his mitzvot.
He who says, "I know him," and doesn't keep his mitzvot, is a liar, and the truth is not in him.
But whoever keeps his word, God's love has most assuredly been perfected in him. This is how we know that we are in him:
he who says he remains in him ought himself also to walk just like he walked.