Deuteronomy 17:14-19

The King 14When you enter the land the LORD your God is giving you and have taken possession of it and settled in it, and you say, “Let us set a king over us like all the nations around us,” 15be sure to appoint over you a king the LORD your God chooses. He must be from among your fellow Israelites. Do not place a foreigner over you, one who is not an Israelite. 16The king, moreover, must not acquire great numbers of horses for himself or make the people return to Egypt to get more of them, for the LORD has told you, “You are not to go back that way again.”

17He must not take many wives, or his heart will be led astray. He must not accumulate large amounts of silver and gold. 18When he takes the throne of his kingdom, he is to write for himself on a scroll a copy of this law, taken from that of the Levitical priests. 19It is to be with him, and he is to read it all the days of his life so that he may learn to revere the LORD his God and follow carefully all the words of this law and these decrees