Sefer Vayikra through Parashat Shemini deals with a description of the divine service and the inauguration of the Mishkan. Parashat Acharei Mot contains a detailed account of the service of Yom Kippur. In our two parshiyot, Tazria and Metzora, a different topic "interrupts": the various causes of tumah (ritual impurity) that affect man. These can be broken into two categories: those that affect men or women without being a response to wrongdoing, such as tumot related to the reproductive cycle; those that can be attributed to man’s wrongdoing, i.e., tzara’at afflicting the body, garments, or structures.
Rashi (Vayikra 12:2) tells us that the laws of man are specified after those of animals, just as man was created after animals. Man, unlike animals, wavers greatly between greatness and lowliness. "If he has merit, he precedes the ministering angels; if he lacks merit, a mosquito precedes him" (Bereishit Rabba 8:1). Since creation was made with man in mind, he has a great obligation to improve the world and not spoil it. He has two opposite sides: he is made of earth and has the spirit of life that Hashem breathed into him. Man stands between his animalistic side and his divine side, between impurity and sanctity. Both elements follow him throughout his life; he should not be naïve and ignore the danger that lurks around his spiritual state.
A child is born, and at the same time there is tumah (Vayikra 12:2). On the eighth day, a Jewish baby boy is circumcised (ibid. 3). Only a baby whose mother has tumah at birth can have his brit on the eighth day even on Shabbat. The connection is that the brit mila is made to fight tumah, for if man does not fight the tumah, it will overtake him spiritually and he will be liable and deserving of the various forms of tzara’at.
Hashem acknowledges that He created evil and attached it to man (see Micha 4:6; Berachot 32a). But it was created so that we should fight and overcome it. We use special "spices" such as Torah (Kiddushin 30b), thus called because like spices change a food’s taste, so Torah turns a person from bad to good.
Sometimes a person errs by being too far away from Hashem, and sometimes he sins by approaching Hashem in the wrong way (see Vayikra 16:1). The latter can come out of arrogance of a type that can lead to lashon hara and tzara’at. Tzara’at comes to signal man about his problem. Fortunate is the one who responds properly to the sign. On a national level as well, there are forces of good and of bad: when one goes up, the other goes down (Megilla 6a).
Why do we tell man that if he is successful, he is greater than the angels? For a similar reason that we tell him he could be lowlier than a fly. Lack of recognition of the dangers in both directions need to be countered. Therefore, we should tell the "Levites" of all generations, i.e., Torah scholars in our times, the power they possess and what they need to do. In such a confusing world, we need to concentrate on logic and a clear head and win the battle over the direction of our lives.