Destroy him that remaineth of the city - i. e., shall destroy those of every city that had previously escaped. The phrase tersely describes a conqueror who first defeats his enemies in battle, and then hunts out the fugitives until he has cut off all of every place (compare 1-Kings 11:16).
The victories of David were a partial accomplishment of the predictions Numbers 24:14, Numbers 24:18, but did not exhaust them.
It is apparent that Edom and Moab are named by Balaam, as they are also by the prophets (compare e. g., Isaiah 11:14), as representatives of the pagan nations Numbers 24:8 who were hostile to the theocracy. As Jacob therefore figures as a constant type of the kingdom of Messiah in the prophets, so do Edom and Joab of the enemies of that kingdom; and in the threatened ruin of Edom and Moab is indicated the eventual destruction of all that resist the kingdom of God in its power.
The "Star" and "Sceptre" of the prophecy, like the "Sceptre" and "Lawgiver" of Genesis 49:10, point also naturally to a line of princes rather than to an individual; or rather are emblems of the kingdom of Israel generally. Thus, the victories of David and his successors, generation after generation, over Edom and Moab, are unquestionably recurring and progressive accomplishments of what Balaam foretold; but in addition the prophecy reaches forward to some further and culminating accomplishment; and that too in "the latter days" Numbers 24:14, the ordinary prophetic designation for the time of the Messiah (compare the marginal references).
To a Christian the connection between the Star and Seeptre of Balaam and the Star of the king of the Jews, which the wise men saw Matthew 2:2, is self-evident.

Out of Jacob shall come, etc. - This is supposed to refer to Christ, because of what is said Genesis 49:10.
It is exceedingly difficult to fix the true sense of this prophecy in all its particulars. Probably the star, Numbers 24:17, is only an emblem of kingly power. Among the Egyptians a star is said to have been the symbol of the Divine Being. The scepter refers to the kingly power in exercise. The corners or outskirts may mean the petty Moabitish governments, as the Chaldee has understood the term. If karkar, which we translate utterly destroy, be not the name of a place here, as it is in Judges 8:10, (which is not very likely), it may be taken in one of those senses assigned to it, (see on Numbers 24:17 (note)), and signify the blending together the children of Sheth, that is, all the inhabitants of the earth; for so the children of Sheth must necessarily be understood, unless we consider it here as meaning some king of the Moabites, according to Grotius, or a city on the borders of Moab, according to Rabbi Nathan. As neither Israel nor the Messiah ever destroyed all the children of men, we must (in order to leave the children of Sheth what they are generally understood to be, all the inhabitants of the world) understand the whole as a prophecy of the final universal sway of the scepter of Christ, when the middle wall of partition shall be broken down, and the Jews and Gentiles become one united, blended fold, under one shepherd and bishop of their souls.
I cannot think that the meteoric star which guided the wise men of the east to Bethlehem can be intended here; nor do I think that Peter refers to this prophecy when he calls Christ the day star, 2-Peter 1:19; nor that Revelation 2:28, where Christ is called the morning star, nor Revelation 22:16, where he is called the bright and morning star, refers at all to this prophecy of Balaam. Nor do I think that the false Christ who rose in the time of Adrian, and who called himself Barcochab, which literally signifies the son of a star, did refer to this prophecy. If he had, he must have defeated his own intention, because the Son of the star is not The Star that should arise, but at the utmost a descendant; and then, to vindicate his right to the Jewish throne, he must show that the person who was called the star, and of whom he pretended to be the son or descendant, had actually reigned before him. As the sun, moon, stars, planets, light, splendours, effulgence, day, etc., were always considered among the Asiatics as emblems of royalty, government, etc., therefore many, both men and women, had these names given to them as titles, surnames, etc. So the queen of Alexander the Great, called Roxana by the Greeks, was a Persian princess, and in her native tongue her name was Roushen, splendor. Hadassah, who became queen to Ahasuerus, in place of the repudiated Vashti, and is called Esther by Europeans in general, was called in the language of Persia Sitareh; from whence by corruption came both Esther, the Persian queen, and our word star. And to waive all farther examples, a Mohammedan prince, at first named Eesouf or Joseph, was called Roushen Akhter when he was raised to the throne, which signifies a splendid or luminous star. This prince, by a joyful reverse of fortune, was brought from a gloomy prison and exalted to the throne of Hindostan; on which account the following couplet was made, in which there is a paronomasia or play on the name Roushen Akhter; and the last line alludes to the history of the patriarch Joseph, who was brought out of prison and exalted to the highest honors in Egypt.
Roushen Akhter bood, aknoon mah shud̀
Yousef az zendan ber amd shah shud.
"He was a bright star, but is now become a moon.
Joseph is brought out of prison, and is become a glorious king."

Out of Jacob shall come he that shall have dominion, and shall destroy him that remaineth of the (m) city.
(m) Of the Edomites.

Out of Jacob shall come he that shall have dominion,.... Meaning either David, or rather the Messiah; and so Jarchi interprets this of another ruler out of Jacob, even of the Messiah, of whom it is said, he shall have dominion from sea to sea; Psalm 72:8,
and shall destroy him, that remaineth of the city; chief city of Edom, or of any of the cities of it, signifying that there should be none left, see Obadiah 1:18, this is also applied to the days of the Messiah, in the ancient writings of the Jews (q).
(q) Bemidbar Rabba, fol. 179. 3.

Out of Jacob shall come he that shall have dominion--David, and particularly Christ.
that remaineth of the city--those who flee from the field to fortified places (Psalm 60:9).

"And a ruler shall come out of Jacob, and destroy what is left out of cities." The subject to ירדּ is indefinite, and to be supplied from the verb itself. We have to think of the ruler foretold as star and sceptre. The abbreviated form וירדּ is not used for the future ירדּה, but is jussive in its force. One out of Jacob shall rule. מעיר is employed in a collected and general sense, as in Psalm 72:16. Out of every city in which there is a remnant of Edom, it shall be destroyed. שׁריד is equivalent to אדום שׁארית (Amos 9:12). The explanation, "destroy the remnant out of the city, namely, out of the holy city of Jerusalem" (Ewald and Baur), is forced, and cannot be sustained from the parallelism.

Out of Jacob - Out of Jacob's loins. He that shall have dominion - David, and especially Christ. Of the city - Or from or out of this city, that is, the cities, the singular number for the plural. He shall not subdue those Moabites and Edomites which meet him in the field, but he shall pursue them even to their strongest holds and cities.