And we write these things in order that our joy may be made complete.

They have gone forth from our midst, but they did not really belong to us; for had they belonged to us, they would have remained with us. But they left us that it might be manifest that professed believers do not all belong to us.

He who believes in the Son of God has the testimony in his own heart: he who does not believe God has made Him a liar, in that he has refused to accept the testimony which God has given about His Son.