That his heart be not lifted up above his brethren, and that he turn not 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)
See ch. 8:2, 14. A man needs the grace of God to avoid becoming high-minded. It is not easy for a king or other leader to think of himself as the servant of his people.
Prolong his days.
See ch. 4:26, 40. Only a truly converted man could order his life according to the obligations outlined for a monarch in this chapter. Guided by the divine instructions recorded in the book of the law, he would become a pattern to his people, a living transcript of God’s will for men.