The tragic end of King Joash is a story of betrayal, assassination, and a dishonorable burial. His death at the hands of his own subjects serves as a clear expression of divine justice, operating strictly on the principle of measure for measure.
The identities of the assassins reveal a deeper layer of meaning. Their mothers were of Ammonite and Moabite descent. The primary approach among commentators is that this specific lineage highlights the theme of ingratitude. Historically, the Ammonites and Moabites showed profound ungratefulness to Abraham, who had saved their ancestor Lot, by later hiring Balaam to curse the Israelites. God chose individuals from these nations to punish Joash because the king himself committed a terrible act of ingratitude. He forgot the kindness of Jehoiada the priest, who had saved his life and secured his crown, and instead murdered Jehoiada's son, the prophet Zechariah [רש״י, רד״ק, אברבנאל].
The assassins were rebellious servants [ביאור שטיינזלץ]. Their goal was not to seize power, as evidenced by the smooth transition of the throne to Joash's son Amaziah in Judah. Rather, they sought to avenge the blood of Zechariah. The nature of the assassination perfectly mirrored the king's own failures. Joash had defiled the house of God and disrespected Zechariah's sacred role as a priest and prophet. In return, his servants defiled the privacy of his royal bedchamber and completely disregarded his authority as king. Just as Joash cast off the authority of God and forgot the loyalty owed to his benefactors, his servants cast off his royal authority and forgot their loyalty to him [אברבנאל].
Following his death, Joash was laid to rest in the City of David, the general burial region for the kings of the Davidic dynasty [ביאור שטיינזלץ]. However, he was not granted a place in the prestigious tombs of the kings, specifically the honored cave where David and Solomon were buried. The people understood that the recent military defeats and national troubles were direct divine punishments for the king's idolatry and his murder of Zechariah. Consequently, they disgraced him in death, intentionally denying him an honorable royal burial [רד״ק, אברבנאל].
The historical record in the Book of Kings leaves out the explicit details of Joash's sins and the murder of Zechariah, opting instead for brief allusions. This is because the narrative focuses primarily on the chronological sequence of events and the succession of royal dynasties. The Book of Chronicles, written later by Ezra, serves as a comprehensive commentary and completion of the history. It specifically documents the underlying moral and spiritual causes of these events, vividly illustrating God's active providence in the world [אברבנאל].