(24) For the border of the children of Ammon was strong.--These words assign the reason why the conquests of the Amorites were arrested, not why the children of Israel did not take possession of the land of the Ammonites, with whom they were forbidden to meddle, and whose land they were not to occupy. (See Deuteronomy 2:19.)

Verse 24. - And Israel smote him with the edge of the sword. This was the first time that generation had seen war, if we except the uncertain episode of the king of Arad, and they could have had no weapons but such as their fathers had brought out of Egypt. It was, therefore, a critical moment in their history when they met the forces of Sihon, confident from their recent victory over Moab. We may suppose that Joshua was their military leader now, as before and after. From Arnon unto Jabbok. The Jabbok, which formed the boundary of Sihon on the north towards the kingdom of Og, and on the east towards the Ammonites, is the modern Zerka: it runs in a large curve northeast, north-west, and west, until it fails into Jordan, forty-five miles north of the mouth of the Arnon. Even unto the children of Ammon: for the border of the children of Ammon was strong. This is perhaps intended to explain rather why the Amorites had not extended their conquests any further, than why the Israelites made no attempt to cross the border of Ammon; they had another and more sufficient reason (see Deuteronomy 2:19). Rabbah of Ammon, which stood upon the right (here the eastern) bank of the Upper Jabbok, was an extremely strong place which effectually protected the country behind it, even until the reign of David (see on 2 Samuel 11, 12).

21:21-35 Sihon went with his forces against Israel, out of his own borders, without provocation, and so ran upon his own ruin. The enemies of God's church often perish by the counsels they think most wisely taken. Og, king of Bashan, instead of being warned by the fate of his neighbours, to make peace with Israel, makes war with them, which proves in like manner his destruction. Wicked men do their utmost to secure themselves and their possessions against the judgments of God; but all in vain, when the day comes on which they must fall. God gave Israel success, while Moses was with them, that he might see the beginning of the glorious work, though he must not live to see it finished. This was, in comparison, but as the day of small things, yet it was an earnest of great things. We must prepare for fresh conflicts and enemies. We must make no peace or truce with the powers of darkness, nor even treat with them; nor should we expect any pause in our contest. But, trusting in God, and obeying his commands, we shall be more than conquerors over every enemy.And Israel smote him with the edge of the sword,.... Slew him and his army, entirely routed them, and got a complete victory over them; God giving them up into their hands, who otherwise were a very strong, powerful, and warlike people; see Amos 2:9.

and possessed his land from Arnon unto Jabbok; two rivers, the one to the south, the other to the north of his country; the one was the boundary of his country between him and the Moabites, the other the boundary of his country between him and the Ammonites, as it follows:

even unto the children of Ammon; for the border of the children of Ammon was strong; which is given as a reason why the Israelites proceeded no further in their conquest; there was another reason for that, which was the order of the Lord not to distress the Ammonites, nor meddle with them; though Jarchi makes this prohibition to be their strength, Deuteronomy 2:19, but this is given as a reason why Sihon could not extend his conquests further, because it was so well fortified, either by nature or art, or both, by the river Jabbok, by mountains and frontier towns, and particularly by Rabbah, as the Targum of Jonathan suggests, which was their royal city in later times, and a very strong place; see 2 Samuel 12:26.