"Temporal Authority: To What Extent It Should Be Obeyed"
I think that's the document everyone is referring to. Or is there another?
Why does Luther always make so much sense? Read the entire thing here. The ending of the treatise was brilliant. Basically is is a call to use your brain and follow natural law and love when the circumstances require it. He relates a memorable story to illustrate his point.
"A good and just decision must not and cannot be pronounced out of books, but must come from a free mind, as though there were no books. Such a free decision is given, however, by love and by natural law, with which all reason is filled; out of the books come extravagant and untenable judgments. Let me give you an example of this.
This story if told of Duke Charles of Burgundy. A certain nobleman took an enemy prisoner. The prisoner's wife came to ransom her husband. The nobleman promised to give back the husband on condition that she would lie with him. The woman was virtuous, yet wished to set her husband free; so she goes and asks her husband whether she should do this thing in order to set him free. The husband wished to be set free and to save his life, so he gives his wife permission. After the nobleman had lain with the wife, he had the husband beheaded the next day and give him to her as a corpse. She laid the whole case before Duke Charles. He summoned the nobleman and commanded him to marry the woman. When the wedding day was over he had the nobleman beheaded, gave the woman possession of his property, and restored her to honor. Thus he punished the crime in a princely way.
Observe: No pope, no jurist, no lawbook could have given him such a decision. It sprang from untrammeled reason, above the law in all the books, and is so excellent that everyone must approve of it and find the justice of it written in his own heart. St. Augustine relates a similar story... Therefore, we should keep written laws subject to reason, from which they originally welled forth as from the spring of justice. We should not make the spring dependent on its rivulets, or make reason a captive of letters."