The Sefarim Hakedoshim ask why the portion of Parah Adumah begins with the pasuk saying that it is the “chukas haTorah”, as if it is the only law in the Torah. Why doesn’t it simply say that it is the “chukas haparah”?
Sefer Kisvei Ramam quotes the Rebbe of Kobrin zy”a as explaining that the entire Torah is comparable to the Parah Adumah. We find that a Parah Adumah purifies people who are tamei but also makes people who were tahor impure. So too, he explains that the Torah does the same.
If someone is “tamei”, meaning that he learns Torah “shelo l’shma”, for impure purposes, or if he is impure in the sense that he is on a low level of ruchnius, still and all, if he learns Torah he will be purified. The Torah that he learns will lift him out of his impure state and make him tahor.
However, Torah can also “make pure people tamei.” If someone is on a high level of ruchnius but he learns Torah “shelo l’shma”, with improper intentions, that Torah will make him tamei. This is as Chazal say (Taanis 7A): “If someone learns Torah l’shma, it is a medicine that provides life for him. But if someone learns Torah shelo l’shma, it becomes a poison of death for him.”