"... that the evils of the present day may be somewhat lessened." Luther

To the Most Illustrious Prince and Lord, Frederick, duke of Saxony, arch-marshal and elector of the Holy Roman Empire, landgrave of Thuringia, margrave of Meissen, His Most Gracious Lord.

Our Lord and Savior Jesus has left us a commandment which applies equally to all Christians, namely, that we are to render humanitarian services, or rather (as the Scriptures call them), the works of mercy [Luke 6:36], to those who are afflicted and in a state of calamity, and that we are to visit the sick, try to free the captives, and do similar things for our neighbor so that the evils of the present may be somewhat lessened. Our Lord Jesus Christ himself gave us the brightest example of this commandment when, because of his infinite love for the race of men, he descended from the bosom of the Father into our misery and our prison, that is, into our flesh and our most wretched life, and took upon himself the penalty for our sins so that we might be saved, as he says in Isaiah 43 [:24], “You have burdened me with your sins, and you have wearied me with your iniquities.”

He who is not moved by this illustrious example and is not driven by the authority of the divine commandment to do such works of mercy will, at the last judgment, deserve to hear the voice of the angry judge, saying, “Depart from me, you cursed ones, into everlasting fire. I was sick, and you did not visit me. With gross ingratitude for the supreme blessings bestowed by me upon you and the whole world, you have not by even the smallest service come to aid your brethren—no, me, Christ, your God and Savior, in the brethren” [Matt. 25:41–45].

Thus, Most Illustrious Prince, since I saw that your Lordship has been stricken with a grave illness and that Christ also is sick in you, I have deemed it my duty to visit your Lordship with this little writing. I cannot pretend that I do not hear the voice of Christ as it cries to me out of your Lordship’s body and flesh, saying, “Look, I am sick.” Such evils as sickness and the like are borne not by us Christians, but by Christ himself, our Lord and Savior, in whom we live and who plainly testifies in the Gospel, “Whatever you have done unto the least of mine, you have done unto me” [Matt. 25:40]. And while we have the duty to visit and console all who are afflicted with sickness, we are especially obligated to those of the household of faith. Paul clearly distinguishes between strangers and those of the household, those bound to us by intimate ties, Galatians 6 [:10].

Luther's Works 42.121