Numbers 21:24 - Joseph Benson’s Commentary on the Old and New Testaments

From Arnon Or, which reached from Arnon; and so here is a description or limitation of Sihon's conquest and kingdom, that it extended only from Arnon unto the children of Ammon And then the following words, for the border of the children of Ammon was strong, come in very fitly, not as a reason why the Israelites did not conquer the Ammonites, for they were absolutely forbidden to meddle with them, (Deuteronomy 3:8,) but as a reason why Sihon could not enlarge his conquests to the Ammonites, as he had done to the Moabites. Jabbok A river by which the countries of Ammon and Moab were in part bounded and divided. Strong Either by the advantage of the river, or by their strong holds in their frontiers.