Death is disguised as a monk and the nun follows quietly along — in contrast to the monk (letter O).
There was nothing new in the thought that good people did not fear Death - who was simply a messenger from God. Holbein might have looked at the dance of death in Klingental (picture to the left) in his own hometown Basel or he might have had a copy of Heidelberg's block book from 1465 (picture below to the right).
The accompanying text for this letter goes: »Eyn weg ist der dem menschen würd gesehen gerecht / aber syne letzten füren in zu dem todt«.
This is from The Book of Proverbs 14:12, which in Luther's version sounds: »Manchem scheint ein Weg recht; aber zuletzt bringt er ihn zum Tode«. In English: »There is a way which seemeth right unto a man, but the end thereof are the ways of death«.