You are children of your God יהוה. You shall not gash yourselves or shave the front of your heads because of the dead.
For you are a people consecrated to your God יהוה: your God יהוה chose you from among all other peoples on earth to be a treasured people.
לא תתגדדו YE SHALL NOT CUT YOURSELVES — i.e. you shall not make cuttings and incisions in your flesh for the dead in the way the Amorites do (Sifrei Devarim 96:11), because you are children of the Lord and it is therefore becoming for you to be comely and not cut about and with hair torn out.
Hosszú szugja, 3 oldal a Talmudban.
Reish Lakish said to Rabbi Yoḥanan: I should read here the verse: “You shall not cut yourselves [titgodedu]” (Deuteronomy 14:1), which is interpreted as meaning: Do not become numerous factions [agudot]. In other words, the Jewish people should be united, rather than divided into disparate groups that act in different ways. Before analyzing this issue, the Gemara asks: This verse: “You shall not cut yourselves,” is required for the matter itself, as the Merciful One is saying: Do not cut yourselves over the dead. How is the halakha concerning factions derived from this apparently straightforward verse?