Matthew 5:7. Blessed are the merciful, for they shall obtain mercy.
This is also an outstanding fruit of faith, and it follows well upon what went before. Anyone who is supposed to help other people and to contribute to the common weal and success should also be kind and merciful. He should not immediately raise a rumpus and start a riot if something is missing or if things do not go as they should, as long as there is still some hope for improvement. One of the virtues of counterfeit sanctity is that it cannot have pity or mercy for the frail and weak, but insists on the strictest enforcement and the purest selection; as soon as there is even a minor flaw, all mercy is gone, and there is nothing but fuming and fury. St. Gregory also teaches us how to recognize this when he says: “True justice shows mercy, but false justice shows indignation.” True holiness is merciful and sympathetic, but all that false holiness can do is to rage and fume. Yet it does so, as they boast, “out of zeal for justice”; that is, it is done through love and zeal for righteousness.11
The whole world is being forced to the conclusion that they have been carrying on their mischief and violence under the lovely and excellent pretext and cover of doing it for the sake of righteousness. In the same way, both in the past and in the present, they have been exercising their enmity and treachery against the Gospel under the guise of defending the truth and exterminating heresy.For this they want God to crown them and to elevate them to heaven, as a reward for those who out of great thirst and hunger for righteousness persecute, strangle, and burn His saints.
They want to make the claim and to give the impression, even more than the true saints, that they hunger and thirst for righteousness. They put up such a good front and use such beautiful words that they think even God Himself will not know any better. But the noble tree is known by its fruits. When they should demand justice, that is, the proper administration of both the spiritual and the temporal realm, they do not do so. It never enters their mind to instruct and improve anyone. They themselves live in continual vice; and if anyone denounces their behavior or does not praise it and do as they want, he must be a heretic and let himself be damned to hell. You see, that is how it is with every counterfeit saint. His self-made holiness makes him so proud that he despises everyone else and cannot have a kind and merciful heart.
Therefore this is a necessary warning against such abominable saints. If a man deals with his neighbor in an effort to help and correct him in his station and way of life, he should still take care to be merciful and to forgive. In this way people will see that your aim really is righteousness and not the gratification of your own malice and anger; for you are righteous enough to deal in a friendly and gentle manner with the man who is willing to forsake his unrighteousness and improve himself, and you tolerate and endure his fault or weakness until he comes around. But if you try all this and find no hope for improvement, then you may give him up and turn him over to those whose duty it is to punish.
Now, this is the one aspect of mercy, that one gladly forgives the sinful and the frail. The other is to do good also to those who are outwardly poor or in need of help; on the basis of Matthew 25:35 ff. we call these “works of mercy.” The arrogant Jewish saints knew nothing about this aspect either. There was nothing in them but ice and frost—yes, a heart as hard as a block of stone—and not a single loving drop of blood that took pleasure in doing good for a neighbor, nor any mercy that forgave sin. All they were concerned about and thought about was their own belly, even though another man might have been starving to death. Thus there is much more mercy among public sinners than there is in such a saint. This is how it has to be; for they praise only themselves and regard only themselves as holy, despising everyone else as worthless and supposing that the whole world must serve them and give them plenty, while they are under no obligation to give anyone anything or any service.
Hence this sermon and exhortation seems contemptible and useless to such saints. The only pupils it finds are those who already cling to Christ and believe in Him. They know of no holiness of their own. On the basis of the preceding items they are poor, miserable, meek, really hungry and thirsty; they are inclined not to despise anyone, but to assume and to sympathize with the need of everyone else. To them applies the comforting promise: “It is well with you who are merciful. For you will find pure mercy in turn, both here and hereafter, and a mercy which inexpressibly surpasses all human kindness and mercy.” There is no comparison between our mercy and God’s, nor between our possessions and the eternal possessions in the kingdom of heaven. So pleased is He with our kindness to our neighbor that for one pfennig He promises us a hundred thousand guldens if we have need of them, and for a drink of water, the kingdom of heaven (Matt. 10:42).
Now, if anyone will not let himself be moved by this wonderful and comforting promise, let him turn the page and hear another judgment: “Woe and curses upon the unmerciful, for no mercy shall be shown to them.” At the present time the world is full of people, among the nobles and city people and peasants, who sin very grievously against the dear Gospel. Not only do they refuse to give support or help to poor ministers and preachers; but besides they commit theft and torment against it wherever they can, and act as if they meant to starve it out and chase it out of the world. Meanwhile they go along quite smugly, supposing that God must keep quiet about it and approve of everything they do. But it will hit them someday. I am afraid that someone will come. along who will make a prophet out of me—for I have given ample warning—and treat them mercilessly, taking away their reputation and their property, their body and their life, so that the Word of God might remain true and so that he who refuses to show or to have mercy might experience endless wrath and eternal displeasure. As St. James also says (James 2:13): “Judgment without mercy will be spoken over the one who has shown no mercy.” At the Last Day, therefore, Christ will also cite this lack of mercy as the worst injury done to Him, whatever we have done out of a lack of mercy. He Himself will utter the curse (Matt. 25:41, 42): “I was hungry and thirsty, and you gave Me no food, you gave Me no drink. Depart from Me, therefore, you cursed, into eternal hell-fire.” He warns and exhorts us faithfully, out of sheer grace and mercy. Whoever does not want to accept this, let him choose the curse and eternal damnation. Think of the rich man in Luke 16; daily he saw poor Lazarus lying before his door full of sores, yet he did not have enough mercy to give him a bundle of straw or to grant him the crumbs under his table. But look how terribly he was requited; in hell he would gladly have given a hundred thousand guldens for the privilege of boasting that he had given him even a thread.
Luther, M. (1999, c1956). Vol. 21: Luther's works, vol. 21 : The Sermon on the Mount and the Magnificat (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.). Luther's Works (21:29). Saint Louis: Concordia Publishing House.