he who is doing the sin, of the devil he is, because from the beginning the devil doth sin; for this was the Son of God manifested, that he may break up the works of the devil;

We [who preach the true Gospel] represent God; the person who knows God listens to our message; the one who does not belong to God does not listen to us. This is how we can know [the difference between those speaking by] the Holy Spirit of truth and [those speaking by] the spirit of [Satan's] error.