King Solomon's execution of Joab serves as a profound act of divine justice, intended to cleanse the House of David from the stain of innocent blood. Rather than a simple legal penalty, this execution provides moral closure for a history of treachery. God is exacting retribution, ensuring that the consequences of the innocent blood Joab shed fall squarely upon his own head [מצודת דוד, ביאור שטיינזלץ].
Joab’s crimes were exceptionally severe, warranting both a death sentence and a generational curse. He assassinated two military commanders with a sword, staging the murders to look like official royal executions. By acting without the king's authorization, he deeply insulted David's honor [מלבי״ם]. These victims are considered more righteous and better than Joab primarily because they refrained from shedding innocent blood, though they likely possessed other superior virtues as well [רד״ק].
Their moral superiority is further highlighted by a historical contrast. When King Saul previously commanded these men to execute the priests of God, they bravely refused. They correctly understood the principle that a royal decree cannot override the word of God. Joab, on the other hand, demonstrated a stark lack of moral boundaries; when David sent him a letter instructing him to arrange the death of Uriah the Hittite, Joab obeyed immediately and without protest [רד״ק].
A critical aspect of this historical reckoning is the absolute exoneration of David. Joab deliberately concealed his violent intentions, acting entirely behind the king's back [מצודת דוד, ביאור שטיינזלץ]. Establishing David's ignorance of these plots was highly necessary due to persistent rumors among the public that the king had secretly orchestrated the assassinations. These suspicions were fueled by political circumstances: one of the victims, Abner, was closely tied to the rival House of Saul, while the other, Amasa, had supported Absalom's rebellion and was appointed by him to a unique military command exclusively over the tribe of Judah [מצודת דוד].
These widespread rumors caused David immense sorrow, forcing him to mourn the commanders publicly to prove he had no hand in their deaths. Ultimately, it is unequivocally established that David knew absolutely nothing about Joab's deadly plans, finally putting the damaging suspicions to rest [רד״ק, אברבנאל].