Ramban

THERE SHALL STEP FORTH A STAR OUT OF JACOB. Because the Messiah will gather together the dispersed of Israel from all the corners of the earth, Balaam compares him [metaphorically] to a star that passes through the firmament from the ends of heaven, just as it is said about [the Messiah]: and behold, there came with the clouds of heaven, one like unto a son of man etc. Balaam thus said that he saw that at a distant time a star would pass from the ends of heaven, and there would rise out of it the sceptre of a ruler, and he shall smite through the corners of Moab, and break down all the sons of Seth, the son of Adam, who was the father of all the nations., Vol. I, p. 98. He mentioned the corners of Moab in order to inform Balak that his people would not fall into the hand of Israel now, but in the end of days Moab will not be saved from the hand of the ruling king [in Israel]. And the meaning of ‘the corners’ of Moab is that this ruler [in Israel] will break down all the sons of Seth, and they [Moab] will not be saved, even though they are cut off on ‘the corner,’ and have no name among the nations, and will not fight against Israel.