Albert Barnes Commentary Numbers 21:29

"Woe to thee, Moab! Thou art undone, O people of Chemosh: He hath given his sons as fugitives, And his daughters into captivity, Unto Sihon king of the Amorites." — Numbers 21:29 (ASV)

Chemosh - The national God of the Moabites. The name probably means “Vanquisher,” or “Master.” The worship of Chemosh was introduced into Israel by Solomon (1 Kings 11:7; 2 Kings 23:13). It was no doubt to Chemosh that Mesha, king of Moab, offered up his son as a burnt-offering (2 Kings 3:26–27).

In the first six lines (Numbers 21:27–28) the poet imagines for the Amorites a song of exultation for their victories over Moab, and for the consequent glories of Heshbon, their own capital.

In the next lines (Numbers 21:29) he himself joins in this strain, which now becomes one of half-real, half-ironical compassion for the Moabites, whom their idol Chemosh was unable to save.

But in the last lines (Numbers 21:30) a startling change takes place; the new and decisive triumph of the poet’s own countrymen is abruptly introduced, and the boastings of the Amorites fade utterly away.

Of the towns, Heshbon was the northernmost and therefore, to the advancing Israelites, the last to be reached. Medeba, now Madeba, was four miles south of Heshbon (Compare 1 Chronicles 19:7 and 1 Chronicles 19:15).