כִּ֭י תְּשִׁיתֵ֣מוֹ שֶׁ֑כֶם בְּ֝מֵֽיתָרֶ֗יךָ תְּכוֹנֵ֥ן עַל־פְּנֵיהֶֽם׃
Sapagkat gagawin mo silang isang bahagi; sa pamamagitan ng iyong mga bagting ng busog ay tututukan mo ang kanilang mga mukha.
Kli Yakar
And I say that when there is peace among the enemies, then the war is most dangerous because they all unite as one against God and His anointed. However, when their hearts are divided and they are not united as one group, the danger is not as great. This is the miracle that the Holy One, blessed be He, performs for Israel: even though at the beginning when they go out to war, all the nations join together as if they were all one horse and rider, like one man, nevertheless, as you approach the battle, in the meantime, God will send confusion among them, and they will separate from one another, and each man’s sword will be against his fellow. As it is written: In one way they will come out against you, but in seven ways they will flee before you (Deuteronomy 28:7). Because at the beginning they are in one accord, but in the meantime God will send confusion among them, causing their hearts to be divided until all seven nations — each one of them — will flee by their own separate way, as it is written: For You will make them turn their back (Psalms 21:13), etc., meaning to divide them into separate parts.
Radak
שכם, another word meaning חלק. The word occurs in the same sense in Psalms 21,13 כי תשיתמו שכם, as well as in Tzefania 3,9 ולעבדו שכם אחד.
Rashi
בחרבי ובקשתי WITH MY SWORD AND WITH MY BOW — When Simeon and Levi slew the inhabitants of Shechem all the surrounding nations gathered together to join in battle against them and Jacob girded on his weapons to war against them (cf. Genesis Rabbah 80:10) Another explanation of this verse: שכם אחד ONE PORTION [ABOVE THY BRETHREN] — this refers to the birthright (Genesis Rabbah 97:6): that Joseph’s children should receive two portions when Canaan would be divided amongst the tribes (cf. Deuteronomy 60:17; Joseph therefore was to be regarded as the first-born). The word שכם signifies portion. “For thou wilt make them שכם” i.e. thou wilt place my enemies before me in portions (thou wilt scatter them before me); (Deuteronomy 60:8) “I will divide שכם the portion”; (Hosea 6:9) “on the way they murder שכמה” i.e. each man kills someone as his own portion; (Zephaniah 3:9) “to serve him as though they were all but one portion (שכם)” i.e. to serve him unitedly.