1 John 4:3

"For whosoever does not confess that Jesus Christ has come in the flesh, is antichrist;" and whosoever does not confess the testimony of the cross, is of the devil; and whosoever perverts the oracles of the Lord to his own lusts, and says that there is neither a resurrection nor a judgment, he is the first-born of Satan. Wherefore, forsaking the vanity of many, and their false doctrines, let us return to the word which has been handed down to us from the beginning; "watching unto prayer," and persevering in fasting; beseeching in our supplications the all-seeing God "not to lead us into temptation," as the Lord has said: "The spirit truly is willing, but the flesh is weak."

No one has as yet fallen in with Elias; no one has as yet escaped from Antichrist; no one has as yet had to bewail the downfall of Babylon.

In like manner, in the passage, "If even an angel of heaven preach unto you any other gospel than that which we have preached unto you, let him be anathema," he calls attention to the artful influence of Philumene, the virgin friend of Apelles. Surely he is antichrist who denies that Christ has come in the flesh. By declaring that His flesh is simply and absolutely true, and taken in the plain sense of its own nature, the Scripture aims a blow at all who make distinctions in it.

Well, but who is the man of sin, the son of perdition," who must first be revealed before the Lord comes; "who opposeth and exalteth himself above all that is called God, or that is worshipped; who is to sit in the temple of God, and boast himself as being God? " According indeed to our view, he is Antichrist; as it is taught us in both the ancient and the new prophecies, and especially by the Apostle John, who says that "already many false prophets are gone out into the world," the fore-runners of Antichrist, who deny that Christ is come in the flesh, and do not acknowledge Jesus (to be the Christ), meaning in God the Creator.

But in his epistle he especially designates those as "Antichrists" who "denied that Christ was come in the flesh," and who refused to think that Jesus was the Son of God.

How can either darkness illuminate, or unrighteousness justify? And when they say that "they are not of God, but are of the spirit of Antichrist"

If a spirit dissolves the divine-human unity of Christ and thinks that the pure Word of God is outside all flesh, and cannot really be a man, and states that everything done in his incarnation is a fantasy, then that spirit is not from God. But someone will say that there are many heretics who do accept the incarnation, the Montanists for instance. The answer to them is that just as no one says that Jesus is Lord except by the Holy Spirit, so the Montanists do not accept all the implications of incarnational belief. For those who say that Jesus is Lord but who do not follow his commandments do not have the Holy Spirit. Although they honor him with their lips, their hearts are far from him.

"Hereby is known the Spirit of God: every spirit that confesseth that Jesus Christ is come in the flesh is of God: and every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is the antichrist, of whom ye have heard that he should come; and even now already is he in this world." Our ears, so to say, are on the alert for discerning of the spirits; and we have been told something, such that thereby we discern not a whit the more. For what saith he? "Every spirit that confesseth that Jesus Christ came in the flesh, is of God." Then is the spirit that is among the heretics, of God, seeing they "confess that Jesus Christ came in the flesh"?

"But he that shall do, and shall teach so, shall be called great in the kingdom of heaven." From this, that He has here said, fecerit, "shall do," while in opposition to this He has there said solverit, meaning non fecerit, "shall not do, and shall teach so" - to break, then, is, not to do - what doth He teach us, but that we should interrogate men's deeds, not take their words upon trust?

This then is the Spirit of God, which saith that Jesus is come in the flesh, which saith, not in tongue but in deeds, which saith, not by making a noise but by loving. And that spirit is not of God, which denies that Jesus Christ is come in the flesh - denies, here also, not in tongue but in life; not in words but in deeds. It is manifest therefore by what we may know the brethren. Many within are in a sort within; but none without except he be indeed without.

Aye, here perchance they lift themselves up against us, and say: Ye have not the Spirit from God; but we confess "that Jesus Christ came in the flesh:" but the apostle here hath said that those have not the Spirit of God, who confess not "that Jesus Christ came in the flesh." Ask the Arians: they confess "that Jesus Christ came in the flesh:" ask the Eunomians; they confess "that Jesus Christ came in the flesh:" ask the Macedonians; they confess "that Jesus Christ came in the flesh:" put the question to the Cataphryges; they confess "that Jesus Christ came in the flesh:" put it to the Novatians; they confess "that Jesus Christ came in the flesh." Then have all these heresies the Spirit of God? Are they then no false prophets? Is there then no deception there, no seduction there? Assuredly they are antichrists; for "they went out from us, but were not of us."

"And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is the antichrist, of whom ye have heard that he should come; and even now already is he in this world." Therefore he saith in the Gospel: "Whoso shall break one of these least commandments, and shall teach so, shall be called least in the kingdom of heaven." What is this breaking? What this teaching? A breaking in the deeds and a teaching as it were in words. "Thou that preachest men should not steal, dost thou steal?" Therefore he that steals breaks or undoes the commandment in his deed, and as it were teaches so: "he shall be called least in the kingdom of heaven," i.e. in the Church of this present time. Of him it is said, "What they say do ye; but what they do, that do not ye."

Nay, and that ye may know that he has referred the matter to deeds, he saith, "And every spirit, qui solvit Christum, which does away with Christ that He came in the flesh, is not of God." A doing away in deeds is meant. What has he shown thee? "That denieth:" in that he saith, "doeth away" (or, "unmaketh"). He came to gather in one, thou comest to unmake. Thou wouldest pull Christ's members asunder. How can it be said that thou deniest not that Christ is come in the flesh, who rendest asunder the Church of God which He hath gathered together? Therefore thou goest against Christ; thou art an antichrist. Be thou within, or be thou without, thou art an antichrist: only, when thou art within, thou art hidden; when thou art without, thou art made manifest. Thou unmakest Jesus and deniest that He came in the flesh; thou art not of God.

What is the spirit that is not from God? That "which denieth that Jesus Christ is come in the flesh." And what is the spirit that is from God? That "which confesseth that Jesus Christ is come in the flesh." Who is he that confesseth that Jesus Christ is come in the flesh? Now, brethren, to the mark! let us look to the works, not stop at the noise of the tongue. Let us ask why Christ came in the flesh, so we get at the persons who deny that He is come in the flesh. If thou stop at tongues, why, thou shalt hear many a heresy confessing that Christ is come in the flesh: but the truth convicteth those men. Wherefore came Christ in the flesh? Was He not God? Is it not written of Him, "In the beginning was the Word, and the Word was with God, and the Word was God"? Was it not He that did feed angels, is it not He that doth feed angels? Did He not in such sort come hither, that He departed not thence? Did He not in such sort ascend, that He forsook not us?

What are we to do then? By what to discern them? Be very attentive; let us go together in heart, and knock. Charity herself keeps watch; for it is none other than she that shall knock, she also that shall open: anon ye shall understand in the name of our Lord Jesus Christ. Already ye have heard that it was said above, "Whoso denieth that Jesus Christ is come in the flesh, the same is an antichrist." There also we asked, Who denies? because neither do we deny, nor do those deny. And we found that some do in their deeds deny; and we brought testimony from the apostle, who saith, "For they confess that they know God, but in their deeds deny Him." Thus then let us now also make the enquiry in the deeds not in the tongue.

Wherefore then came He in the flesh? Because it behooved us to have the hope of resurrection shown unto us. God He was, and in flesh He came; for God could not die, flesh could die; He came then in the flesh, that He might die for us. But how died He for us? "Greater charity than this hath no man, that a man lay down his life for his friends." Charity therefore brought Him to the flesh. Whoever therefore has not charity denies that Christ is come in the flesh. Here then do thou now question all heretics. Did Christ come in the flesh? "He did come; this I believe, this I confess." Nay, this thou deniest. "How do I deny? Thou hearest that I say it!" Nay, I convict thee of denying it. Thou sayest with the voice, deniest with the heart; sayest in words, deniest in deeds.

"How," sayest thou, "do I deny in deeds?" Because the end for which Christ came in the flesh, was, that He might die for us. He died for us, because therein He taught much charity. "Greater charity than this hath no man, that a man lay down his life for his friends." Thou hast not charity, seeing thou for thine own honor dividest unity. Therefore by this understand ye the spirit that is from God. Give the earthen vessels a tap, put them to the proof, whether haply they be cracked and give a dull sound: see whether they ring full and clear, see whether charity be there. Thou takest thyself away from the unity of the whole earth, thou dividest the Church by schisms, thou rendest the Body of Christ. He came in the flesh, to gather in one, thou makest an outcry to scatter abroad.

And this is the Antichrist of whom you have heard that he comes, etc. He comes with the imminent day of judgment, born into the world as that man more wicked than all others, the son of iniquity. And now he is already in the world, dwelling in the minds of those who resist Christ either by profession or by deed, without the remedy of repentance.

And every spirit that dissolves Jesus is not from God. He dissolves Jesus who denies either His divinity, or His soul, or His flesh, which the Catholic faith teaches that He truly has. He also dissolves Jesus who, by perversely interpreting or by perverse sight, corrupts the commands and words of Jesus. But also he who disturbs the unity of the holy Church, which Jesus came to gather, strives, as far as is in him, to dissolve Jesus. Nor is it surprising if such are not from God, who disband the works, words, or sacraments of God. For they are so far from God, that some of them who wished by evil doctrine to separate the divinity of Christ from human dispensation, have also erased this verse, where it is said, "And every spirit that dissolves Jesus is not from God," from this Epistle, lest their error be convicted by the authority of blessed John. Finally, Nestorius revealed that he did not know this sentence was inserted into the authentic copies, and therefore he did not fear to dissolve Jesus, and thus render himself foreign to God, saying that the blessed Virgin Mary was not the mother of God, but only of a man, such that he made another person of the man, another of the Deity; nor did he believe in one Christ in the Word of God and in flesh and soul, but preached separately another Son of God, another of man.

Beloved, do not believe every spirit, but test the spirits to see whether they are from God; for many false prophets have gone out into the world. By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God; and every spirit that does not confess Jesus is not from God. This is the spirit of the Antichrist, of which you heard that it is coming, and now it is already in the world.
After John has completed his discourse on love for one's neighbor, and has demonstrated that this is a sign of the permanence of the Spirit we have received, he now adds a judgment concerning those who are truly brothers and neighbors, so that having this, we do not fall into the occasion of the commandment of love concerning false brothers, false apostles, and false prophets, bringing great harm upon ourselves from this.
Indeed, by embracing them as if they were of similar character, we will first harm ourselves while we communicate with those who are faithless, and we present holy things to dogs (Matt. 7:6): then, to those who associate with us, our love towards them will persuade many to take them as teachers and to believe what is said by them, while not observing, as if they were stealthily drawn away because of their conduct with us, and what is the indication of these, this is what follows:
"every spirit that confesses." Every spirit, whether of prophecy or the dignity of apostleship, that Jesus Christ has come in the flesh, is from God: but whatever does not confess this is not from God, but this dignity is of the Antichrist, of which you have heard.
When? From these words which he said a little earlier, that many antichrists are in the world, (1 Jn. 2:18) that is, forerunners of the Antichrist. Furthermore, he says that the confession of the Lord's coming is not made by the tongue, but by works. How? As blessed Paul says: "Always carrying in the body the death of Jesus, so that the life of Jesus may also be made evident in our body." (2 Cor. 4:10) Therefore, whoever has Jesus working in him, and is dead to the world, no longer lives to the world but to Christ, and carries Him not only in the flesh of Christ, but also in his own, he is from God. But whoever lives not for Christ, but for the world, that is, for the pleasures of the world, such a person is not from God. Therefore, Paul says, "When there are contentions and factions among you, are you not carnal and walking according to man?" (1 Cor. 3:3) He who walks according to the flesh does not have the spirit of Christ (Rom. 8:9); that is, he who does not live according to Christ, in such a way that he has died to the world, this one is not of Christ.
"and now it is already in the world." In the world, John says, the Antichrist is already present, not physically, but because of the presence of those who prepare the way for him, namely, false prophets, false apostles, and heretics. This Antichrist, however, will be a man who conveys Satan, exalted against all that is called God or divinity. (2 Thess. 2:4)
Therefore, he will also reject the worship of idols, which he signified as gods: moreover, by adding this: Every divine being also signifies Christianity: and he will only attempt to show himself as God.

The antichrist will be a man who bears Satan inside him and who exalts himself above everything which is called God or which is worshiped. For that reason he will spurn idolatry and demand that people worship him instead.