Deuteronomy 17:20

20 so that his heart is not high above his brethren, and so as not to turn aside from the command, right or left, so that he prolongeth days over his kingdom, he and his sons, 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 `And it hath been, when he sitteth on the throne of his kingdom, that he hath written for himself the copy of this law, on a book, from [that] before the priests the Levites,

19 and it hath been with him, and he hath read in it all days of his life, so that he doth learn to fear Jehovah his God, to keep all the words of this law, and these statutes, to do them;

20 so that his heart is not high above his brethren, and so as not to turn aside from the command, right or left, so that he prolongeth days over his kingdom, he and his sons, in the midst of Israel.