Deuteronomy 17:20

20 that his heart be not lifted up above his brethren, that he depart not from the commandments on the right hand or on the left; that he and his sons may reign long in his dominion among the children 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 when he shall be established in his government, then shall he write for himself this repetition of the law into a book by the hands of the priests the Levites;
19 and it shall be with him, and he shall read in it all the days of his life, that he may learn to fear the Lord thy God, and to keep all these commandments, and to observe these ordinances:
20 that his heart be not lifted up above his brethren, that he depart not from the commandments on the right hand or on the left; that he and his sons may reign long in his dominion among the children of Israel.

Footnotes 1

The Brenton translation of the Septuagint is in the public domain.