Death comes to the duke in the guise of a woman - wearing a bonnet. Behind the duke is a flag draped coffin on a stretcher — the same coffin that stands behind the nobleman in Holbein's great dance of death. The horror is painted in the Duke's face; in contrast to the young woman there is no erotic subtext here.
Holbein probably found the inspiration for this picture in his own earlier work, the Holbein Dagger (picture to the left). But even if he may have been inspired by the image of his own older work, the meaning is quite different.
On the dagger sheath, Death has stolen the woman's bonnet in order to ape and mock his victim. In the case of the duke, there's no aping of course. The message is rather the grotesque thought that a fragile woman with a bonnet (and hanging breasts) is able to inspire such terror in the mighty army-leader. Holbein might have gotten that idea from Heidelberg's dance of death, where a frail woman easily overpowers the armoured knight.
The accompanying text for this letter goes: »Du würst nitt herab stygen von dem bettlin / vff welches du bist gestigen / aber du wurst sterben des todts«.
This line appears thrice in 1st chapter of 2nd Kings, which in Luther's version sounds: »[...] Du sollst nicht mehr von dem Bett herunterkommen, auf das du dich gelegt hast, sondern sollst des Todes sterben [...]«. In English: »[...] Thou shalt not come down from that bed on which thou art gone up, but shalt surely die [...]«.