The life of King Joash ends in a tragic and agonizing downfall, serving as a direct punishment for his deep ingratitude and cruelty toward those who had cared for him most. Following an attack by the Aramaean army, the invading forces withdrew, but not out of any mercy. They deliberately left the king behind suffering from severe injuries and diseases, intending for him to remain broken, helpless, and in agony [מצודת דוד, ביאור שטיינזלץ].
While the king lay in this highly vulnerable state, his own servants conspired and launched a rebellion against him [מצודת ציון, ביאור שטיינזלץ]. Their uprising was driven by a desire for revenge. They sought justice for the murder of Zechariah, the son of Jehoiada the priest, whom the king had killed while completely disregarding the tremendous kindness and loyalty that Jehoiada had shown him in the past [רש״י].
Although the historical events focus on the murder of Zechariah alone, the revenge is framed as a response to the spilled blood of Jehoiada's children, in the plural. Some commentators explain this as a common biblical figure of speech, where a plural concept is used even when referring to a single individual [מצודת דוד, רד״ק, חומת אנך]. Others suggest that the king might have actually executed Zechariah's brothers as well, punishing them for supporting him [רד״ק, ביאור שטיינזלץ, חומת אנך]. A third perspective proposes that the plural form encompasses not only Zechariah's own life but also the lives of all the descendants who would have been born to him throughout future generations [חומת אנך].
The king's assassination was an exact, measure-for-measure punishment. He was killed while lying sick and in pain upon his own bed [מלבי״ם, ביאור שטיינזלץ]. Just as Zechariah was murdered while feeling calm and secure—trusting that he would be treated with respect due to his father's legacy—the king met a sudden and violent end in the one place he expected to be most quiet and safe [רש״י, חומת אנך].
Even in death, the king faced ultimate humiliation. Although he was buried within the City of David, he was deliberately excluded from the tombs of the kings. He was laid to rest in disgrace outside the royal burial plot, serving as a final punishment for his wicked actions and reflecting his bitter end as a defeated, humiliated ruler stripped of all honor [ביאור שטיינזלץ].