וְאַתָּה֙ תֶּאְזֹ֣ר מָתְנֶ֔יךָ וְקַמְתָּ֙ וְדִבַּרְתָּ֣ אֲלֵיהֶ֔ם אֵ֛ת כָּל־אֲשֶׁ֥ר אָנֹכִ֖י אֲצַוֶּ֑ךָּ אַל־תֵּחַת֙ מִפְּנֵיהֶ֔ם פֶּֽן־אֲחִתְּךָ֖ לִפְנֵיהֶֽם׃
Tú pues, ciñe tus lomos, y te levantarás, y les hablarás todo lo que te mandaré: no temas delante de ellos, porque no te haga yo quebrantar delante de ellos.
Rashi
and the loins of kings I will loosen This is an expression of weakness and breaking strength, for girding the loins constitutes arming with strength. Comp. (Job 38:3) “Gird up your loins like a mighty man”; (Jer. 1:17) “And you gird up your loins”; (Job 12:21) “And the belt of the mighty He loosens”; an expression of breaking strength.