Commentary for Deuteronomy 17:20

ולבלתי סור מן המצוה AND THAT HE DEPART NOT FROM THE COMMANDMENT — not even from a less important command given to him by means of a prophet.

THAT HIS HEART BE NOT LIFTED UP ABOVE HIS BRETHREN. Here in the Torah a prohibition against conceit is alluded to, for Scripture prohibited even the king from indulging in conceit and haughtiness of heart, surely other people who are not of such commendable excellence [or merit, are forbidden to be haughty]. Scripture has thus admonished him for whom it is proper to be haughty and majestic that his heart must be as humble as that of his brethren of lower status, because conceit is a reprehensible character-trait, and it is loathsome to G-d even in a king. To G-d alone is the greatness¹²⁹See ibid., Verse 11. and exaltation,¹³⁰See Nehemiah 9:5. and to Him alone is the praise, and in [the knowledge of] Him may man glory, as the matter is explained by King Solomon, Every man that is proud in heart is an abomination to the Eternal.¹³¹Proverbs 16:5. It is further written, But let him that glorieth glory in this, that he understandeth, and knoweth Me.¹³²Jeremiah 9:23.

that he may not be haughty which would occur, if he were above the law.