Luther: "God is curing this evil with that thorn of Satan, to show me that I am nothing."

Thus the Lord says of His people in Jer. 49:12: “If those who did not deserve to drink the cup must drink it, will you go unpunished,” Even though Daniel and his companions endured the captivity among the heathen, nevertheless they had not deserved the captivity because of their sins, as the others had.

Similarly, in the revolt of the peasants many very fine men perished, not because they were just as guilty as the rebels but because they were among the rebels. For disasters never occur among a people without also affecting the godly. These are being tested, but the others are being judged.

Then, too, the godly are often afflicted, not because their sins deserve it or because they are being tested, but in order that they may be kept humble and may not be puffed up on account of their gifts. Thus Paul says about himself that a thorn in the flesh was given to him to keep him from becoming conceited because of his extraordinary revelations. “An angel of Satan,” says he, “beats me with his fist that I may not exalt myself” (2 Cor. 12:7). It is as though he were saying: “Because of my superb gifts I might rate myself above all the other apostles and perhaps look down upon them; but God is curing this evil with that thorn of Satan, to show me that I am nothing and to cause me to humble myself.”

This is also the reason why the church, which God has endowed with the most excellent gifts of the forgiveness of sins, the Holy Spirit, and eternal life, experiences such manifold dangers and misfortunes. If it enjoyed these gifts without affliction, it would become proud and boastful.

Thus you may observe that frequently a pious and godly person is afflicted with a variety of perils and misfortunes in quick succession, when, on the other hand, for the wicked and ungodly everything turns out in accordance with their hearts desire.

This inequitable state of affairs often gives rise to resentment in the saints. But if you consider the situation rightly, you are enduring these hardships for your own great good; for if you had no affliction, you would become proud and would be condemned. Now when God ties want, scorn, sickness, a vexatious wife, and disobedient children to your neck like a heavy stone, you are not what the Greeks call ὑπερήφανος or proud; but you take it patiently, and you do not look down upon those who are less gifted than you. These discussions about the causes of misfortunes are profitable, for they supply not only knowledge but comfort as well.

Luther on Gen. 12:20, LW vol. 2.