Young children, it is the last hour: and as ye have heard that antichrist comes, and now many antichrists have come; whence we know that it is the last hour.

Who is a liar if not he denying that Jesus is the Christ? He is antichrist, denying the Father and the Son.

And every spirit which acknowledges not Jesus Christ having come in the flesh is not of God: and this is that of antichrist which ye have heard comes; and now is already in the world.

For many cheats come into the world, they not acknowledging Jesus Christ coming in the flesh. This is the cheat and antichrist.