כִּ֣י שֵׁ֧שֶׁת חֳדָשִׁ֛ים יָֽשַׁב־שָׁ֥ם יוֹאָ֖ב וְכָל־יִשְׂרָאֵ֑ל עַד־הִכְרִ֥ית כָּל־זָכָ֖ר בֶּאֱדֽוֹם׃
Sechs Monate waren Joab und ganz Israel dort geblieben, bis alle männlichen Idumäer ausgerottet waren.
Rabbeinu Bahya
אראנו ולא עתה, “I can see it — but not now.” The prophecy being introduced refers to David who four hundred years from this date would smash the nobles of Moav. The words וקרקר כל בני שת, “and undermine the children of Sheth,“ is a reference to mankind as such which is descended in the main from the descendants of Sheth, Adam’s third son Noach being one of them. (Compare Samuel II 8,2 where David’s victory over Moav is documented.)
Another way of understanding the reference by Bileam to the “descendants of Sheth.” The word שת may not refer to a human being but to “foundation.” We find the word שתין meaning “the foundations of the earth” in Talmudic language, a reference to the “navel” of the earth under the Holy Temple. Bileam foresaw that David’s victories would create havoc among the existing world order in the countries surrounding the land of Israel. The words “and Edom will become a conquest” also apply to that period as we know from Kings I 11,16 that Edom”s males were wiped out by David’s general Yoav. The words (verse 19) וירד מיעקב mean that someone descended from Yaakov will arise and destroy the remnants of all the cities of Edom. This may be a veiled reference to Rome. Finally, the words וירד מיעקב also mean that the messiah will be descended from Israel. The words ולא יהיה שריד לבית עשו, “no remnant will remain of Esau,” in Ovadiah 18 are the logical conclusion of Bileam’s prophecy here.
Another way of understanding the reference by Bileam to the “descendants of Sheth.” The word שת may not refer to a human being but to “foundation.” We find the word שתין meaning “the foundations of the earth” in Talmudic language, a reference to the “navel” of the earth under the Holy Temple. Bileam foresaw that David’s victories would create havoc among the existing world order in the countries surrounding the land of Israel. The words “and Edom will become a conquest” also apply to that period as we know from Kings I 11,16 that Edom”s males were wiped out by David’s general Yoav. The words (verse 19) וירד מיעקב mean that someone descended from Yaakov will arise and destroy the remnants of all the cities of Edom. This may be a veiled reference to Rome. Finally, the words וירד מיעקב also mean that the messiah will be descended from Israel. The words ולא יהיה שריד לבית עשו, “no remnant will remain of Esau,” in Ovadiah 18 are the logical conclusion of Bileam’s prophecy here.
Rashi
Egypt etc. and Edom—He juxtaposed them as regards their retribution. You find that, were it not for Egypt, Edom would not exist, as it is stated: (I Kings 11:16 21) “For Joab and all Israel remained [stationed] there for six months etc. every male in Edom.” And it is stated there: (verse 17) “Adad fled, he and some Edomite men etc. And Hadad pleased Pharaoh very much etc. And Hadad etc. that David slept with his fathers etc.” And, at the end, (verse 25) “And he was an adversary to Solomon (sic).” Said the Holy One, blessed be He: I will destroy both of them.
Chizkuni
וירד מיעקב, “and out of Yaakov one shall have dominion.” A dictator will arise from Yaakov and destroy the last vestige of the Edomites. Bileam refers to David’s general Yoav, of whom it has been reported in Kings I 11,16: “for Yoav and all Israel stayed there for six months until they had killed off every male member of the Edomites.” וירד מיעקב, “of this man it is said: “he will not leave a remnant of the house of Esau.” (Ovadiah, 18)
Rashi
And they smote the remnant... that had escaped from being annihilated by David, for David destroyed every male in Edom.