Commentaire sur Le Deutéronome 14:2

כי עם קדוש אתה FOR THOU ART AN HOLY PEOPLE — You are holy — your actual holiness comes to you from your fathers, but, in addition, ובך בחר ה׳ THE LORD HAS CHOSEN YOU [so that you are for two reasons bound to keep away from these pagan customs] (cf. Sifrei Devarim 97:1).

סגולה מכל העמים, this is why G’d prohibits your disfiguring yourself. He did not prohibit this to the Gentiles, as they are not as special as you are.

For you are a sacred people to Hashem, your God. The verse gives two reasons for the prohibition of lacerating with a utensil or making a bald spot with your hand as a sign of mourning. 1. Because you are sacred people to Hashem, meaning separate and elevated. Therefore you must know that every pain or difficult event that happens to you is the will of Hashem, or to atone for sin, which is also part of the Glory of Hashem and His will. One who is set aside for service of Hashem should set aside his personal pain for the will of Hashem. However, crying and mourning according to the appropriate measures that the Torah gave is the will of Hashem, to give honor to the deceased, to the extent that the honor of the deceased overrides all the mitzvos in the Torah. But acting in a way which leaves a lasting mark after the time that the Torah gave for mourning is not honor for the deceased, but simply an expression of grief. It is not appropriate for those who are sacred to Hashem to act in this way. 2. Hashem chose you. You should gather all those who come to worship Hashem from the other nations. If so, it would not be giving glory to Hashem before the other nations of the world if His chosen people were lacerated or bald.