פּירוש אויף שמות 32:26

מי לה' אלי means, WHOEVER IS FOR THE LORD let him come TO ME.

ויאספו אליו כל בני לוי, “all the members of the tribe of Levi rallied around him.” According to the plain meaning of the text, the relatives of Moses, members of his tribe would not allow someone from another tribe to usurp Moses’ authority.

!מי לה' אלי, “anyone who is on G–d’s side to me!” Moses called on all the Israelites who had not become involved with the golden calf in any way to join him. He was immediately joined by all the members of the tribe of Levi. The entire male population of the tribe, none of whom had been counted, joined him. No other tribe, of those that had been numbered, was loyal in its entirety. This is reflected in Deuteronomy 33,9 (Moses’ blessings of the people) where the Torah writes concerning the tribe of Levi: האומר לאביו ולאמו לא ראיתיו ואת אחיו לא הכיר ואת בניו לא ידע---כי (כולם) שמרו אמרתך, “who can say of his father and his mother: “I have not seen him,” (take part in the sin of the golden calf) nor did he see his brother (do so) nor did his son have any knowledge (of that sin) for they all were loyal to Your word.” Moses was not able to compliment any other tribe similarly. It appears that one reason for this great loyalty was the fact that Moses was their tribe’s leader, and they did not wish to trade him for a leader from a different tribe. Maimonides, in his treatise on idolatry chapter 1, near the end, states that Avraham had already handed the Torah in oral form to his son Yitzchok, who transmitted it to Yaakov, who in turn transmitted it to his son Levi. The latter’s sons already founded a Torah study academy, so that knowledge of the Torah’s laws never was interrupted even during the many years of bondage in Egypt. It appears that the attitude to the golden calf by the different sections of the people was divided into three different groups; one group accepted the golden calf by promising to follow it to wherever it would lead the people, אשר ילכו לפנינו; they only wished for the golden calf to be leader on their journeys. The second group accepted the golden calf as a symbol of idolatry; this group made up the three thousand Israelites who were killed by the Levites. The third group was the entire tribe of Levi which completely rejected the golden calf in all its aspects, remaining completely loyal to Hashem.

כל בני לוי ALL THE SONS OF LEVI — All the sons — from this we may gather that all the tribe of Levi remained worthy men (consequently “slay every man his brother” in the next verse can refer only to one who was his brother from the same mother, as explained by Rashi there) (Yoma 66b).