The king of Israel, however, had rules quite different from kings of other nations, for the ideal king of Israel would be both a spiritual and a political ruler. Therefore, God gave Israel “royal rules” (Deuteronomy 17:14-20):
First and foremost, a king of Israel had to be an Israelite, no matter how attractive a foreign candidate might seem.
Regardless of the king’s fortune, God also declared that he may not own a multitude of horses. Nor was he to have a multitude of wives, no matter how politically helpful the alliances might be. In these two laws, perhaps God was trying to warn the future King Solomon of his downfall. But Solomon for all his wisdom, did not heed this advice (see Second Book of Kings).
God also directed that the king, once enthroned, must write two copies of the Torah, one to be placed in his treasury and one to have with him at all times. The constant presence of the Torah was intended to teach the king to fear God, “to keep all the words of this law and these statutes … that his heart not be lifted up above his brothers, and that he not turn aside from the commandment, to the right hand, or to the left; to the end that he may prolong his days in his kingdom, he and his children, in the midst of Israel” (Deuteronomy 17:20)