Deuteronomy 17:20

20 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 Meaning and Commentary

Deuteronomy 17:20

That his heart be not lifted up above his brethren
On account of his office, the dignity of it, considering that he was subject to the law of God, and accountable to the Lord for all his actions:

and that he turn not aside from the commandment, to the right hand or
to the left;
not in the least deviate from the law of God in the whole of his conduct, and particularly in the exercise of his kingly office:

to the end that he may prolong his days in his kingdom;
ruling well according to the laws of God being the way to rule long:

he and his children in the midst of Israel;
this shows, as Jarchi observes, that if his son was fit for the kingdom, he was to be preferred to any other man; for though it was elective, yet to be continued in the same family, provided they walked in the ways of the Lord, and observed his laws.

Deuteronomy 17:20 In-Context

18 It shall be, when he sits on the throne of his kingdom, that he shall write him a copy of this law in a book, out of [that which is] before the priests the Levites:

19 and it shall be with him, and he shall read therein all the days of his life; that he may learn to fear Yahweh his God, to keep all the words of this law and these statutes, to do them;

20 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.