John Calvin on 1 John 4:3

3. And this is that spirit of Antichrist The Apostle added this, to render more detestable the impostures which lead us away from Christ. We have already said that the doctrine respecting the kingdom of Antichrist was well known; so that the faithful had been warned as to the future scattering of the Church, in order that they might exercise vigilance. Justly then did they dread the name as something base and ominous. The Apostle says now, that all those who depreciated Christ were members of that kingdom.

And he says that the spirit of antichrist would come, and that it was already in the world, but in a different sense. He means that it was already in the world, because it carried on in secret its iniquity. As, however, the truth of God had not as yet been subverted by false and spurious dogmas, as superstition had not as yet prevailed in corrupting the worship of God, as the world had not as yet perfidiously departed from Christ, as tyranny, opposed to the kingdom of Christ, had not as yet openly exalted itself, he therefore says, that it would come.

1 John 4:4-6

4. Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.

4. Vos ex Deo estis, filioli, et vicistis eos; quia major est qui est in vobis, quam qui in mundo.

5. They are of the world: therefore speak they of the world, and the world heareth them.

5. Ipsi ex mundo sunt; propterea ex mundo loquuntur, et mundus eos audit.

6. We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.

6. Nos ex Deo sumus; qui novit Deum, audit nos; qui non est ex Deo, non audit nos: in hoc cognocimus spiritum veritatis et spiritum erroris.