King David's final instructions to his young son Solomon present a complex political and moral challenge. He must decide how to handle a powerful, highly decorated military commander who acted with violence and disloyalty. During his own lifetime, David refrained from punishing Joab out of a sense of personal obligation and because the nation relied heavily on his military expertise. Instead, David passes this heavy responsibility to Solomon [ביאור שטיינזלץ, אהבת יהונתן].
David advises his son to act with political wisdom. The primary approach among commentators is that David instructs Solomon not to execute Joab immediately, but rather to wait for a new, justified legal reason to act. While Joab deserved death for needlessly murdering two military leaders, he also held a record of tremendous achievements in fighting God's wars. Therefore, Solomon needs tact to punish him in a way that will not stir up public anger. Other perspectives view this instruction differently, seeing it as a call for political independence. They suggest David is warning the new king not to surrender to Joab's overwhelming power and experience, but to guide the kingdom using his own intellect rather than relying on the commander's advice [אברבנאל]. Another unique approach suggests that Solomon should use his wisdom to determine when Joab is nearing the end of his life. Only then should he be punished, ensuring the nation does not lose his military contributions prematurely [אהבת יהונתן].
The practical goal of David's command is to prevent Joab from dying a natural, peaceful death in his bed. The primary approach among commentators agrees that Solomon must overlook Joab's advanced age and ensure he is killed in the exact manner he used to kill others [מצודת דוד, רד״ק]. This public execution is intended to serve as a severe deterrent, instilling fear to prevent any future rebellions against the crown [רלב״ג].
Beyond the legal and political reasons, there is also a spiritual dimension of atonement. Meeting his end by human hands in this world is meant to cleanse Joab of his sins, ultimately saving him from spiritual punishment and hell in the next world [רש״י, אהבת יהונתן]. However, a more moderate viewpoint argues that David never actually decreed a death sentence. According to this line of thought, David merely wanted Solomon to strip Joab of his power, exile him, and ensure his remaining days were not spent in comfort [אברבנאל]. Similarly, some suggest that David left the specific nature of the punishment entirely up to Solomon's discretion, with the sole requirement being that Joab's final days would not be peaceful [מלבי״ם].