Sforno on Deuteronomy 33:9/ספורנו על דברים ל״ג:ט׳

1האומר לאביו, during the episode of the golden calf,

2ואת בניו לא ידע כי שמרו אמרתך, he showed no personal consideration for his closest family members when it involved carrying out G’d’s commandment. When speaking of the Levites’ children, Moses refers to their performing the rite of circumcision on their sons even in the desert, though many babies died through infections contracted after they had been circumcised, so that the other tribes did not perform this rite in the desert. Our sages in Yevamot 72 claim that the northerly wind did not blow during those 40 years [except at midnight according to some, Ed] and that without the therapeutic effect of the northerly wind the babies would have been at risk.

3ובריתך ינצורו, as our sages confirm in Yuma 66 that the members of the tribe of Levi never became guilty of worshipping idols. This distinction proved itself both in Egypt and in the desert.