1 John 4:2, By this we know the spirits of God:every spirit which confesses that Jesus Christ has come in the flesh is of God.
Whatever they teach, compare it with these words from 1 Tim. 1:15: “Jesus came into this world to save sinners.” You must understand that whatever agrees with this is of God. But you must believe that whatever does not agree with this is from the father of lies (John 8:44). First the Jews deny constantly that Christ came in the flesh, and Cerinthus kept denying that Christ existed before Mary. If He came into the flesh, it follows that He existed before the flesh. He who denies that He came into the flesh denies that He is God and man. Accordingly, he is not of God but is of the devil. Nor is the spirit of the pope of a better sort. For the pope confesses the statement that Christ came in the flesh, but he denies its fruits. But this is the same as saying that Christ did not come in the flesh. For Christ’s coming in the flesh did not take place in order that He might be made man for His own sake; it took place in order that He might save us. He who teaches that Christ came in this way for His own sake destroys the fruit and the efficacy of His coming. For Christ came to destroy the works of the devil (3:8), to redeem sinners from sins. But the pope denies this. To be sure, he keeps the same words; but he denies the efficacy of His coming, that is, that our hearts should trust in Christ’s righteousness alone and be justified. In his bulls the pope condemns the article that we are justified solely by the righteousness of Christ. Yet this is the effect of His incarnation. But Paul contradicts the pope clearly when he says in Rom. 3:28: “We hold that man is justified apart from the works of the Law.” And our John says in 1 John 1:7: “His blood cleanses us from all sin.” Therefore Peter, in 2 Peter 2:1, condemns those who “deny the Master who bought them.” To be sure, they confess the Master; but they deny that He bought them. Therefore we conclude from this text that the spirit of the pope is of the devil; for he denies that Christ came in the flesh, inasmuch as he denies the power and the efficacy of Christ’s coming. I, too, have seen some spirits who indeed confessed Christ by name but actually denied Him. For they said that they believed in God yet not in a mediator.2 But I have nothing before God and cannot think of God without knowing that Christ is His Son and the Mediator of the whole world. Thus one must begin with the coming of Christ, and when stating the causes of salvation one must flee for refuge to Him who comes in order that we may hear His voice when He says in Ps. 40:7: “Lo, I come.”
“Therefore let no one think of God without the Mediator. Consider how Philip errs when he says: “Show us the Father” (John 14:8). Christ said to him: “Philip, he who sees Me has seen the Father” (cf. John 14:9). Therefore let us abide in such a way that we receive Him as the One who comes in the flesh. He seeks the lost sheep. Let us, who are the lost sheep, follow the Shepherd. The spirit of the Sacramentarians denies grossly that Christ came in the flesh when they say that Christ’s “flesh profits nothing” (John 6:63),3 likewise that the spirit must do everything, that Baptism amounts to nothing. Therefore he is not of God. If you consider the papacy, you will not see why Christ came into the flesh. Indeed, you will regard this as superfluous. When Erasmus discusses in one of his epistles why Christ came into the flesh, he makes Him a lawgiver.4 All the monks do the same thing. But Christ came to rescue us from Satan, death, and sin, from which we could not be rescued by our own strength. Yes, He came to remove all laws, to abrogate all righteousnesses, and to establish only His own righteousness. Satan, of course, cannot bear the content of the words but tries to divest them of their power. The pope removes the kernel of Christ and leaves the words; he leaves Him the shell and takes out the kernel. For he confesses the righteousness of Christ, yet in such a way that our righteousness is not removed. And this is no confession at all. We know that there is no approach to God unless, as Paul says in Rom. 5:1, “we are justified by faith.” Christ has flesh, but in it there is the full Divinity. God has offered Himself to us in Christ. Christ came into the flesh to be with us in Baptism and at the Holy Supper. Every spirit who is at pains to teach that Christ does everything through the sacraments is of God, is glad to hear about Christ, and gives thanks. For he understands that Christ is his and that He came in the flesh. Therefore this has been stated emphatically: Behold, this is the test of a spirit, whether he is of God or of the devil. (Luther’s Works vol. 30, p.284-285)