I heard today that the Chazzon Ish says that the reason Parshas Parah is m'doraisa (See here) is because of the pasuk: והזהרתם את בני ישראל מטמאותם "And you shall separate the children of ...
I have read in many places that Parah could be a bliblical requirement to read. Why is that? Zachor makes sense (as it says so in the Torah here). Why Parah?