Concerning the Ammonites, thus saith the LORD; Hath Israel no sons? hath he no heir? why then doth their king inherit Gad, and his people dwell in his cities?
The event of the prophecy as to Ammon preceded that as to Moab (note Jeremiah 49:3); and in Ezekiel 21:26-28 the destruction of Ammon is subjoined to the deposition of Zedekiah.
Hath Israel ... no heir? - namely to occupy the land of Gad, after itself has been carried away captive by Shalmaneser. Ammon, like Moab, descended from Lot, lay north of Moab, from which it was separated by the river Arnon, and east of Reuben and Gad (Joshua 13:24-25), on the same side of Jordan. It seized on Gad when Israel was carried captive. Judah was by the right of kindred the heir, not Ammon; but Ammon joined with Nebuchadnezzar against Judah and Jerusalem (2 Kings 24:2), and exulted over its fall (Psalms 83:4-8; Zephaniah 2:8-9). It had already, in the days of Jeroboam the Second, king of Israel, in Israel's affliction, tried to "enlarge its border," but was punished by the same Jeroboam who "restored the coast of Israel from the entering of Hamath into the sea of the plain, according to the word of the Lord ... by Jonah the son of Amittai" (2 Kings 14:25-26; Amos 1:1; Amos 1:13).
Their king shall go into captivity - (Amos 1:15) referring to Melchom, their tutelary idol (Zephaniah 1:5, "Malcham"); and so the Septuagint reads it here as a proper name (1 Kings 11:5; 1 Kings 11:33; 2 Kings 23:13). The Ammonite god is said to do what they do-namely, occupy the Israelite land of Gad. To Yahweh, the theocratic "King" of Israel, the land belonged of right; so that their Moloch or Milchom was a usurper-king.
His people - the people of Melchom, "their king." Compare "the people of Chemosh," as the designation of Moab, Jeremiah 48:46.