Numbers 21:13

מגבל האמרי The word גבול denotes boundary-line of (marking) the end of their frontier. Similar is the term the גבול of Moab (in this verse): it is an expression for extremity and end. מעבר ארנון ON THE OTHER SIDE OF ARNON — they travelled round the land of Moab along the whole of its southern and eastern sides until they came to the other side of the Arnon into the land of the Amorites on the north of the land of Moab. היצא מגבל האמרי [ARNON WHICH IS IN THE WILDERNESS] THAT COMETH OUT OF THE BOUNDARY OF THE AMORITES — a strip of land jutted out from the territory of the Amorites — it belonged to the Amorites — and entered into the territory of Moab extending unto the Arnon which is the boundary of Moab. It was there that the Israelites encamped and thus they did not pass into the territory of Moab, כי ארנון גבול מואב, FOR ARNON IS THE BOUNDARY OF MOAB, and they did not grant them permission to pass through their land. And although Moses did not state this plainly, Jephtha plainly stated it], as Jephtha said, (Judges 11:17) "And in like manner he sent unto the king of Moab, out he would not permit him to pass through his territory”. Moses, however, made an allusion to it when he stated, (Deuteronomy 2:29) “As the children of Esau that dwell in Seir, and the Moabites that dwell in Ar, did unto me”. What was the case with these (the children of Esau)? They did not permit them to pass through their land, but they made them travel right round it! Similarly, too, Moab did!

מִשָּׁם֮ נָסָ֒עוּ֒ וַֽיַּחֲנ֗וּ מֵעֵ֤בֶר אַרְנוֹן֙ אֲשֶׁ֣ר בַּמִּדְבָּ֔ר הַיֹּצֵ֖א מִגְּבֻ֣ל הָֽאֱמֹרִ֑י כִּ֤י אַרְנוֹן֙ גְּב֣וּל מוֹאָ֔ב בֵּ֥ין מוֹאָ֖ב וּבֵ֥ין הָאֱמֹרִֽי׃

From thence they removed, and pitched on the side of Arnon which is in the wilderness that comes out of the border of the Emori: for Arnon is the border of Mo᾽av, between Mo᾽av and the Emori.