When the king heard thereof. The text varies here. Some manuscripts have "that king," to whom the rejection of his messengers was a personal insult. The Sinaitic, Vatican, and other authorities omit ἀκου ìσας, "heard thereof," and it may well be a gloss from the human view that the king, not being personally present, must have been informed of the incidents.
At the same time, the King, regarded as God, needs no report to acquaint him with what is going on. He was wroth. The injury was done to him, and he resents it (comp. Luke 10:16; John 12:48). His armies.
The Romans, under Vespasian and Titus, the unconscious instruments of his vengeance. So the Assyrians are called "the rod of God's anger" (Isaiah 10:5; Isaiah 13:5; comp. Jeremiah 25:9; Jeremiah 51:20).
Some regard the "armies" as angels, the ministers of God's punishment, especially in war, famine, and pestilence, the three scourges which accomplished the ruin of the Jews. Probably both angels and men are included in the term.
Destroyed … burned up their city. No longer his city, but theirs, the murderers' city, Jerusalem. So a little later foretelling the same fate, Jesus speaks of "your house" (Matthew 23:38). The Romans, in fact, some forty years after, put to the sword the inhabitants of Jerusalem, and burned the city to ashes.