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)

Luther’s Works, Vol. 35, p.253,  Preface to the Psalter

The Psalter ought to be a precious and beloved book, if for no other reason than this: it promises Christ’s death and resurrection so clearly—and pictures his kingdom and the condition and nature of all Christendom—that it might well be called a little Bible. In it is comprehended most beautifully and briefly everything that is in the entre Bible. It is really a fine enchiridion or handbook. In fact, I have a notion that the Holy Spirit wanted to take the trouble himself to compile a short Bible and book of examples of all Christendom or all saints, so that anyone who could not read the whole Bible would here have anyway almost an entire summary of it, comprised in one little book….

A human heart is like a ship on a wild sea, driven by the storm winds from the four corners of the world. Here it is stuck with fear and worry about impending disaster; there comes grief and sadness because of present evil. Here breathes a breeze of hope and of anticipated happiness; there blows security and joy in present blessings. These storm winds teach us to speak with earnestness, to open the heart and pour out what lies at the bottom of it. He who is stuck in fear and need speaks of misfortune quite differently from him who floats on joy; and he who floats on joy speaks and sings of joy quite differently from him who is stuck in fear. When a sad man laughs or a glad man weeps, they say, he does not do so from the heart; that is, the depths of the heart are not open, and what is in them does not come out.

What is the greatest thing in the Psalter but this earnest speaking amid these storm winds of every kind? Where does one find finer words of joy than in the psalms of praise and thanksgiving? There you look into the hearts of all the saints, as into fair and pleasant gardens, yes, as into heaven itself. There you see what fine and pleasant flowers of the heart spring up from all sorts of fair and happy thoughts toward God, because of his blessings. On the other hand, where do you find deeper, more sorrowful, more pitiful words of sadness than in the psalms of lamentation? There again you look into the hearts of all the saints, as into death, yes, as into hell itself. How gloomy and dark it is there, with all kinds of troubled forebodings about the wrath of God! So, too, when they speak of fear and hope, they use such words that no painter could so depict for you fear or hope, and no Cicero or other orator so portray them.

And that they speak these words to God and with God, this, I repeat, is the best thing of all. This gives the words double earnestness and life. For when men speak with men about these matters, what they say does not come so powerfully from the heart; it does not burn and live, is not so urgent. Hence it is that the Psalter is the book of all saints; and everyone, in whatever situation he may be, finds in that situation psalms and words that fit his ease, that suit him as if they were put there just for his sake, so that he could not put it better himself, or find or wish for anything better.

14. I know that whatever God does endures forever; nothing can be added to it, nor anything taken from it; God has made it so in order that MEN SHOULD FEAR BEFORE HIM.

That is: “I have seen that everything God does lasts forever, but our works are unsure and vain.” And one must note the antithesis. He says that only God can carry out His counsels and set a definite time for them. To whom He has given this gift of finding enjoyment in the present, he has it. He is faithful and sure; whatever He gives, no one takes away. If He grants life, no one snatches it away, even though the world and Satan should rage; for He is sure and eternal. If He gives me good eyes, I shall keep them, even though Satan should sprinkle all the dust of the earth into them. If He gives me healthy and robust arms or legs, no one will deprive me of them. All our works have their appointed time, which we do not set. Who sets it, then? God Himself determines this time—not fortune or fate, as the philosophers suppose. When He who made the time permits it to come, then it comes.

Why, therefore, does He afflict men with this vain supposition when He has reserved the appointed time for things to Himself? For this reason, he says, in order that men should fear, that we should not be rash in our works or attempt things proudly and presumptuously as though they came from us. Thus also Paul teaches (Rom. 9:16; Phil. 2:12–13): “Walking in fear, so that you know that it does not depend upon man’s will or exertion, because He Himself is at work both to will and to work.” Anyone who believes this, that matters have not been placed into our hands, will not do anything rashly, but will attribute everything to God in His working and will expect everything from Him. If He grants it, he enjoys it; if He does not, he does without it; and if He takes it away, he bears it. Thus there abide the glory of God and our humiliation and the true worship of God among us. This is what it means to fear God: to have God in view, to know that He looks at all our works, and to acknowledge Him as the Author of all things, both good and evil. (Luther’s Works, v.15 p.54-55)