Musar zu Dewarim 17:20

Pride is the coin which the Great King, Blessed be He, voided, and about which He warned us in His Torah, as it is said: "Take care lest you forget the Lord your God and fail to keep His commandments" (Deut. 8:11). For the arrogant person forgets his Maker, as it is written, "… and (when) your herds and flocks have multiplied, and your silver and gold have increased, and everything you own has prospered, beware lest your heart grow haughty and you forget the Lord your God … and you say to yourselves, 'My own power and the might of my own hand have won this wealth for me'" (Ibid. 8:13-18). And in the case of a king it is said: "Thus he will not act haughtily towards his fellows or deviate from the Instruction to the right or to the left…" (Ibid. 17:20). If the Torah warned against pride even in the case of a king, so much more does it warn ordinary men that they should not attempt to lord over one another.

“That he will not act haughtily toward his brothers” (Deuteronomy 17:20). We were warned with this to remove the trait of pride from our souls; and that the great not lord it over the small, but rather be of a lowly spirit. And pride is one of the weighty sins that lose and destroy the soul, as it is stated (Proverbs 16:5), “Every haughty person is an abomination to the Lord.” And of what help is the procurement of his money, his great wealth and his (lofty) treasures [in the heights]? Behold, since he is loathsome and foul, the heights of his great splendor are lower than the pit. And [even] a wise man should not glory in anything besides the service of God, may He be blessed, and fear of Him, trust in Him, love of Him and clinging to Him - as it is stated (Deuteronomy 10:21), “He is your Glory and He is your God.” And it is [also] stated (Jeremiah 9:22-23) “Let not the wise man glory in his wisdom, etc. But only in this should one glory: In his earnest knowledge of Me.”