פּירוש אויף דברים 17:17

ולא ירבה לו נשים NEITHER SHALL HE MULTIPLY WIVES TO HIMSELF only eighteen, for we find that David had six wives, and it was announced to him (by Nathan the prophet): “[Thus saith the Lord … I gave thy master’s wives into thy bosom] … and if that had been too little, I would add unto thee such and such as these (i.e. twice as many)” (Sanhedrin 21a).

וזהב לא ירבה לו, “and he is not to amass gold for himself.” Rashi understands this imprecise instruction to mean that he must not amass more gold than necessary in order to pay the wages of his soldiers. (Sifri)

that his heart not turn in the pursuit of his lusts.

וכסף וזהב לא ירבה לו מאד NEITHER SHALL HE GREATLY MULTIPLY TO HIMSELF SILVER AND GOLD — but only as much as he needs for his soldiers’ pay (Sanhedrin 21b).