The Torah is written in the world of Atzilus, in Atzilus it's always Shabbos so their is very little mention of it in the Torah, however Tzaras reflects someone only wanting to come closer to Hashem - a Rotzoi without Shuv. (Which was the mistake that Nadav and Avihu made).

To purify Tzaras you need a spiritual person that at the same time is completely Batul to Hashem - a Kohen, and these days our Rebbe.