As always, it is a delight to explore Dr. Luther’s writings. There has been some interesting conversation here on prayers for the dead, which are, only very briefly and tangentially referred to in the Apology as being "not useless" leading some of my friends to conclude that here the Lutheran Church has as a doctrine that prayers for the dead are appropriate. I’m not so sure about that. Another person wrote to inquire what Dr. Luther has to say, after I quoted the second Martin, Dr. Chemnitz. Well, I did a bit of looking about and came up with, not surprisingly, different opinions at different times from Dr. Luther. I believe the best thing he said was that it is best simply to stick with the clear Word of God and therefore not do it. Elsewhere he was willing to concede that it is ok to say a prayer, once or twice, by way of private devotion, but never in the way of some formal, regular praying for the dead. With apologies for the sloppy formatting of these quotes from Luther. Here you go:

20. And Jacob set up a pillar upon her grave; it is the pillar of Rachel’s tomb, which is there to this day.
The fathers decorated sepulchers magnificently. They did not throw away the dead like the bodies of beasts, but they set up memorials of them for a perpetual and immortal reminder so that they might be testimonies of the future resurrection, which they believed and expected. Therefore funeral ceremonies and the funeral procession are to be retained, and likewise the weeping and sympathy, not that there should be prayers for the dead, as Lyra wishes,37 or that we should fear death, but rather that in death itself we should learn to exercise faith as it struggles against the terrors of death and think that we indeed die and are buried in dishonor but that we will rise again in glory. Jacob, for example, retained this consolation: “You have been disappointed in your hope of joys in this life, my Rachel, but what a happy disappointment, because you have exchanged bodily or perishable blessings for eternal blessings.” The pillars were erected to this end, that by the example of the fathers we may learn to neglect and despise the present life for the sake of the other better life which remains. Then, too, in reliance on the promises, we should endure God’s will with equanimity. For what can the devil or the Turk do, even if they take away our life? If we believe that Jesus died and rose again, so also God will bring with Him those who have fallen asleep through Jesus, as 1 Thess. 4:14 says.

Source:  Martin Luther, vol. 6, Luther’s Works, Vol. 6 : Lectures on Genesis: Chapters 31-37, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 6:273 (Saint Louis: Concordia Publishing House, 1999, c1970).

How should the sorcerers have power over the saints who rest securely in the hands of God? But if anyone says: in this way purgatory will also be denied, I answer: if you do not believe in a purgatory, you are not therefore a heretic. The Scriptures know nothing of it. It is better that you disbelieve what is not taught in the Scriptures, than that you reject what is found in the Scriptures. Let the pope and papists be as angry as they will. They have made an article of faith of purgatory because it has brought them the world’s riches—and sent innumerable souls into hell, since they placed their reliance on works and consoled themselves with the thought that works would bring them release. God has given no command concerning purgatory; he has commanded you not to consult the dead nor to believe what they say. Accept God as more reliable and truthful than all angels, and let the pope and his papists keep silence, the more so since their doctrines are lies and deceit which do little to inspire faith in purgatory. I will not stop you if you desire to offer prayers for the dead. In my opinion purgatory is not our common lot, as they teach; I think very few souls get there. Nevertheless, as I said, there is no danger at all for your soul if you do not believe in purgatory. You are not obliged to believe more than what is taught in the Scriptures.9 If here, too, they should cite Gregory, Augustine, and other saints and their pronouncements, glosses, and examples concerning purgatory, I remind you of what you heard earlier,10 namely, to what extent we should follow those dear saints and believe what they say. Who can convince us that they were not deceived in this matter or did not err as in many other matters? Our faith must have a foundation which is God’s word, and not sand or moss, which are the delusions and works of men.

Source:  Martin Luther, vol. 52, Luther’s Works, Vol. 52 : Sermons II, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 52:180 (Philadelphia: Fortress Press, 1999, c1974).

And purgatory is the greatest falsehood, because it is based on ungodliness and unbelief; for they deny that faith saves, and they maintain that satisfaction for sins is the cause of salvation. Therefore he who is in purgatory is in hell itself; for these are his thoughts: “I am a sinner and must render satisfaction for my sins; therefore I shall make a will and shall bequeath a definite amount of money for building churches and for buying prayers and sacrifices for the dead by the monks and priests.” Such people die in a faith in works and have no knowledge of Christ. Indeed, they hate Him. We die in faith in Christ, who died for our sins and rendered satisfaction for us. He is my Bosom, my Paradise, my Comfort, and my Hope.

Source:  Martin Luther, vol. 52, Luther’s Works, Vol. 52 : Sermons II, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 52:180 (Philadelphia: Fortress Press, 1999, c1974).

But theologically the active and speculative life should be defined in a much different manner. For this is such, especially at the present time, that one’s eyes brim with tears. For it does not consist of pleasant speculations and consolations, such as those of the monks; but he who wants to be an Israel and conquer God must be engaged in those exercises of which we spoke previously, namely, begging, seeking, knocking, and retaining the Word and the promise. This is the true speculative life of the godly, where reason and imagination fail, where the senses and understanding are mortified with all their powers, and where a man lives solely by the Word of God. It is written in Deut. 8:3: “He humbled you and let you hunger and fed you with manna, which you did not know, nor did your fathers know; that He might make you know that man does not live by bread alone, but that man lives by everything that proceeds out of the mouth of the Lord.”
Other speculations of the monks are imaginings, cold, dead, and dangerous because they proceed from their own will and reason, without the Word and the promise. Therefore they are to be avoided. He who wants to speculate about GOD successfully in a godly manner should not do it without the Word but should apprehend the incarnate Son and begin from the manger and the swaddling clothes in which He was wrapped until he comes to the ascent into heaven. In this way he will receive in faith and remain in the Word and the promise which has been given. I have known some who boasted about their speculations that they were so captivated by the pleasant nature of these speculations that it seemed to them that they were caught up and lifted up to heaven, as it were. I do not approve of such experiences and do not desire them for myself, because they are without the Word and those who follow after them are men ignorant of the Law and the Gospel.

McCain:  Martin Luther, vol. 6, Luther’s Works, Vol. 6 : Lectures on Genesis: Chapters 31-37, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 6:261 (Saint Louis: Concordia Publishing House, 1999, c1970).

The same thing happens to true and faithful pastors today. The peasants and the citizens give them no more than black bread, and, as Is. 30:2026 says, they eat the bread of adversity and drink the water of affliction. Consequently, God is provoked to anger and permits them to contrive false forms of worship, Masses, purgatory, indulgences, and prayers to the dead, as Paul says in 2 Thess. 2:10–12: “Because they refused to love the truth and to be saved, therefore God sends upon them a strong delusion, to make them believe what is false, so that all may be condemned who do not believe the truth but had pleasure in unrighteousness.” This is the source of such an increase in the prestige and power of the pope and the bishops, who today are rulers and lords of the world. For what reason? It is not because they preach the Gospel, is it? It is not because they care for souls, is it? By no means! Then why? Because they set up the idols of indulgences and Masses. This is by far the richest source of gain. With it they have established societies, monasteries, and most splendid palaces for which the
wealth of the Turks would not suffice. They refused to listen to the true pastors.   

Source:  Martin Luther, vol. 8, Luther’s Works, Vol. 8 : Lectures on Genesis: Chapters 45-50, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 8:230 (Saint Louis: Concordia Publishing House, 1999, c1966).

This is why I have always admonished, as Christ is doing here, that the salt should remain salt and not lose its taste, that is, that we properly teach the chief article of faith. Where this is gone, no other part can stay right, and everything is lost. There can be no faith or understanding any more, and no one can teach or counsel correctly. In brief, a person has to let everyone’s feet trample over him. As we have said, there is no bacchanal or jackass too coarse to gain a great following of believers if he can just think up something new. What is there that the miserable monks have not brazenly dared to preach? They have duped the people with their brother-hoods, little prayers, rosaries, and with the mangy hoods which they put on the dead to promise them heaven.21 What is that but to let everyone’s feet trample over you and to be at the mercy of every preacher of lies? The reason for this is the fact that the devil has conquered the heart and utterly destroyed it with his rotten, damnable doctrines and superstition. Christ is gone, and the knowledge of Christ is lost.
If I keep the conviction that only Christ is my Righteousness and Holiness, no monk will ever delude or beguile me with his cowl, his rosary, or any of his other works or man-made baubles. Faith makes me a judge over every class and way of life that men can think up, and I can condemn anything claiming to show me something else that avails before God. If I neglect this treasure and let it slide in order to look for other ways to be pious, to reconcile God, and to atone for sin, then I am a ready victim for all the various snares and traps of the devil, and have become his obedient servant. Then someone comes along who preaches to me: “If you want to be pious and serve God, put on a cowl, pray this many rosaries every day, light this many little candles to St. Anne.” And I fall for it like a blind man, like everyone’s fool and prisoner. I do whatever I am told, and I cannot avoid even the slightest mistake.
Here Christ Himself has predicted and warned that it would be this way. There has never been a person who knew how to be on guard against this. If we do not keep watch and take care to retain this article, we, too, shall eventually retain no article properly and purely. We shall not stop erring and splitting into sects till it is all over, till preaching and teaching become completely useless and we are nothing but swine and cattle. Alas, that is how it is already among the great crowd, as a result of our contempt and ingratitude for the Gospel.

Source:  Martin Luther, vol. 21, Luther’s Works, Vol. 21 : The Sermon on the Mount and the Magnificat, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 21:60 (Saint Louis: Concordia Publishing House, 1999, c1956).

Source:  Martin Luther, vol. 21, Luther’s Works, Vol. 21 : The Sermon on the Mount and the Magnificat, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 21:60 (Saint Louis: Concordia Publishing House, 1999, c1956).

Another question was raised about the intercession of saints, whether the dead pray for us. Luther replied, “Let’s permit them to pray! Yet both their life and their prayer are unknown to us. We can’t understand how their death is life. If it should be objected that St. Ambrose made an entreaty in behalf of Emperor Theodosius26 after the latter’s death, this was an invention of his. If it should be objected that Augustine prayed for his mother Monica [after her death], this proves nothing, nor did he wish his writings to be adhered to unless they agreed with the Holy Scriptures, for he wrote, ‘I do not wish that my writings,’ etc.27 In short, it’s necessary to stick to the clear Word of God and not to human opinions.” 

Source:  Martin Luther, vol. 54, Luther’s Works, Vol. 54 : Table Talk, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 54:259 (Philadelphia: Fortress Press, 1999, c1967).

As for the dead, since Scripture gives us no information on the subject, I regard it as no sin to pray with free devotion in this or some similar fashion: “Dear God, if this soul is in a condition accessible to mercy, be thou gracious to it.” And when this has been done once or twice, let it suffice. For vigils and requiem masses and yearly celebrations of requiems are useless, and are merely the devil’s annual fair.

Source:
Martin Luther, vol. 37, Luther’s Works, Vol. 37 : Word and Sacrament III, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works, 37:369 (Philadelphia: Fortress Press, 1999, c1961).