Parshas Chukas
“This is the chok of the Torah.” (Bamidbar 19:2)
Rav Yosi Bar Chanina said: Hashem said to Moshe “To you I’m revealing the reason for parah [adumah] but for others it’s a chok.” (Midrash Rabbah 19:6)
Yet the Torah does state in several places that the parah adumah was atoning for the egel.
Furthermore if there is a reason for the mitzvah of parah adumah why did Hashem conceal it from man even from Shlomo Hamelech the wisest of all men?