1 John 4:2 Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
3 And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
These two verses begin by telling us that the spirit of God came in the flesh to this earth in the form of man. It is said that the blood of child comes from the father so Jesus might have been born of human but he His blood was that of God. This is important because our blood cannot cleanse us from our sin but only the blood of Jesus. Everyone who believes this is a child of God. Like wise in verse 4 we see that those who do not believe and confess Jesus came in the flesh and gave His life that we might have eternal life with him is not a child of God but an antichrist. If you know much about the Bible you know it says the antichrist will come but he is already here in anybody who does not believe Jesus is the only to God.