When a leader's top general commits an unauthorized murder, the resulting stain threatens the entire kingdom. To clear himself and his rule from the guilt of this crime, David places a severe, multi-generational curse on the perpetrator, Yoav, and his family. This ensures that the heavy consequences of the murder will rest permanently upon the one truly responsible. The burden of guilt is directed not just at Yoav, but at his father's entire household, because his family members actively advised, assisted, and supported him in carrying out the murder [מצודת דוד, רד״ק]. David asks that this punishment never cease, ensuring that Yoav's descendants will carry this mark forever [מצודת דוד].
The core of this curse consists of five severe punishments, structured around a profound principle of reversal. A righteous person typically merits passing down five specific qualities to his children: strength, beauty, wisdom, a long life, and wealth. Seeing that Yoav's descendants were destined for wickedness, David strips them of these exact blessings, replacing them with their absolute opposites in a strict measure for measure approach [רד״ק, מלבי״ם].
Instead of strength, the descendants are cursed to suffer from a draining bodily illness [מצודת ציון]. In place of beauty, they are struck with leprosy, a disease that causes profound physical ugliness. The blessing of wisdom is replaced with a state of helplessness, though commentators view this loss in different ways. Some understand it as a severe physical impairment, where the person must lean heavily on a cane or crutch due to a crippling leg disease [רש״י, מצודת דוד, מצודת ציון, רד״ק]. Others interpret it as a lack of skill or outright foolishness, leaving the person unable to hold a respectable profession and forcing them to survive on simple, domestic spinning work traditionally associated with women [מלבי״ם, ביאור שטיינזלץ, רד״ק]. To counter the blessing of a long life, David curses them to fall by the sword and die young. Finally, instead of wealth, they are condemned to a life of extreme poverty, lacking even basic bread.
Despite the intensity of David's words, there is a deep historical irony in how this plays out. Because David cursed Yoav unjustly—given that David himself would eventually order Yoav's execution later on—these five severe curses ultimately rebounded. Over the generations, all five punishments ended up striking David's own descendants [רד״ק].