The Alter Rebbe explains that in order to correct the Tzaraas caused by a “Yearning” without a “Returning,” it is not enough to properly fulfill the aspect of “Returning” to reveal Hashem in the world through learning Torah and doing Mitzvos. Since his “Yearning” (the “Intellect of the Mother”) also became blemished by separating it from a “Return,” the only way to correct that blemish is to re-experience his “Yearning” in the correct way, where it is connected to a “Return” (the “Intellect of the Father”). Simply, this means that since he channeled his desire into a yearning to escape the world, but without feeling the responsibility of doing what Hashem wants from him, he has to go back and change his original feelings and approach. He needs to realize that in order to truly connect to Hashem and leave the limitations of the world, he needs to do what Hashem wants from him in this world, through learning Torah and doing Mitzvos as much as possible. He needs to change his attitude and re-channel his passion into making Hashem’s plan happen. And he needs to see that this is infinitely more valuable than just feeling good and having a mystical and spiritual experience.
Based on this concept, the Alter Rebbe explains our verse as follows: "זאת תהיה תורת המצורע" - With this process, the Torah study of the Metzora (who has “Yearning” without “Returning”) will be lasting and complete. "והובא אל הכהן" - He should arouse his “Yearning” to leave the limitations of the world and be included in the truth of Hashem, and bring that “Yearning” to the state of “a Kohen,” to a state of humility and ego deflation, where he realizes that he should direct his passion toward fulfilling Hashem’s plan. Then - "ויצא הכהן" He should bring his rectified, “Kohen-like” passion into actually learning Torah and fulfilling Mitzvos.
