1 John 4:3

3 and every spirit which does not confess Jesus is not of God. This is the spirit of antichrist, of which you heard that it was coming, and now it is in the world already.

1 John 4:3 Meaning and Commentary

1 John 4:3

And every spirit that confesseth not
The proper deity and sonship of Christ, his true and real humanity, and his Messiahship; or any of his offices, doctrines, and ordinances; or his satisfaction and righteousness; or that peace, pardon, justification, life, and salvation, are by him; all which are meant by what follows,

that Jesus Christ is come in the flesh:
this clause is left out in the Ethiopic version, and that without hurting the sense, since it is easily supplied from the preceding verse; and the Alexandrian copy, and the Vulgate Latin version, only read "Jesus": and the latter reads the whole thus, "and every spirit that dissolves Jesus"; that separates the two natures, human and divine, in him, and makes two persons of them; or denies either of them, either that he is truly God, or really man, or denies him to be Jesus, the Saviour; who, as much as in him lies, destroys his person, office, and work, and makes void his obedience, sufferings, and death:

is not of God;
neither he nor his doctrine are of God; his doctrine cannot come from God, being contrary to the word of God; and he himself is neither born of God, nor on his side.

And this is that [spirit] of antichrist:
who is against Christ, or opposes himself to him; as he who denies his sonship, his deity, his humanity, his offices, and his grace, manifestly does; every doctrine that is calculated against these truths is the spirit and doctrine of antichrist:

whereof you have heard that it should come, and even now already is
it the world;
in the false teachers, the forerunners of antichrist; (See Gill on 1 John 2:18).

1 John 4:3 In-Context

1 Beloved, do not believe every spirit, but test the spirits to see whether they are of God; for many false prophets have gone out into the world.
2 By this you know the Spirit of God: every spirit which confesses that Jesus Christ has come in the flesh is of God,
3 and every spirit which does not confess Jesus is not of God. This is the spirit of antichrist, of which you heard that it was coming, and now it is in the world already.
4 Little children, you are of God, and have overcome them; for he who is in you is greater than he who is in the world.
5 They are of the world, therefore what they say is of the world, and the world listens to them.
Revised Standard Version of the Bible, copyright 1952 [2nd edition, 1971] by the Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.