Musar zu Dewarim 10:21

“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.”

Then, one will be clean from striving for the praise and lauding of other people when serving G-d. His thought will turn solely to our Master (G-d), who is our praise, and who is all our good and perfection, and beside Whom there is nothing else, as it is written: "He is your praise and He is your G-d" (Devarim 10:21).

This stems from a lack of true in-depth study and thought on the part of these practitioners [of the shells of piety]. For they did not toil and strain themselves to attain a clear and correct knowledge of the way of G-d. But instead, they went and adopted whatever practices struck them as being pious according to first thought, without delving deeply into the matters and weighing them on the scales of wisdom.