Luther’s writings on vocation

I have been charged with putting together some curriculum on Luther’s writings on vocation. This teaching, of course, is scattered throughout his voluminous works, but I need to pull together some primary sources. My task is complicated by the habit of Luther scholars of referring to his works by volume and page number from his collected works, often the German edition, instead of by the title of his book or sermon. (Could Luther scholars agree not to do that, or, rather, to give the title of the work, as well as where it can be found in the collected works?)

Anyway, Frank Sonnek put me onto this sermon, which is a good example of what I am looking for and is available online. It’s Luther’s sermon on the NINETEENTH SUNDAY AFTER TRINITY, preached in Marburg in 1529. Here is a paragraph on vocation. I will also throw in a paragraph on the kingdom of Christ just because it is so beautiful and profound. Both quotes show Luther at his stylistic best:

Our foolishness consists in laying too much stress upon the show of works and when these do not glitter as something extraordinary we regard them as of no value; and poor fools that we are, we do not see that God has attached and bound this precious treasure, namely his Word, to such common works as filial obedience, external, domestic, or civil affairs, so as to include them in his order and command, which he wishes us to accept, the same as though he himself had appeared from heaven. What would you do if Christ himself with all the angels were visibly to descend, and command you in your home to sweep your house and wash the pans and kettles? How happy you would feel, and would not know how to act for joy, not for the work’s sake, but that you knew that thereby you were serving him, who is greater than heaven and earth. . . .

Therefore we are to regard the kingdom of Christ as a large, beautiful arch or vault which is everywhere over us, and covers and protects us against the wrath of God; yea, as a great, extended firmament which pure grace and forgiveness illuminate and so fill the world and all things, that all sin will hardly appear as a spark in comparison with the great, extended sea of light; and although sin may oppress, it cannot injure, but must disappear and vanish before grace.

Now let me ask for your help. What are some other Luther writings on vocation? “Freedom of the Christian,” of course. “Whether Soldiers Too Can Be Saved.” The catechisms. What else? What sermons and postils and commentaries? What is the source of the oft-quoted but seldom sourced quotation about how changing a baby’s diaper is a holier work than that of all the monks in all the monasteries?