I write to you, not because you do not know the truth, but because you know it, and you know that no lie comes from the truth. 22Who is the liar but the one who denies that Jesus is the Christ?* This is the antichrist, the one who denies the Father and the Son.
This seems to put great weight on the word liar. Anyone who lies about Jesus is the anti-Christ. pretty heavy stuff and strong words for the time.