A recurring theme in Parshas Emor is the incompatibility of the Beis HaMikdosh and tumah. The Kohanim, those designated to serve in the Beis HaMikdosh must refrain from contact with a dead body which constitutes the highest level of tumah. Although a regular Kohein does defile his sanctity to bury his immediate relatives, the Kohein Gadol, whose bond to the Beis HaMikdosh is greater, is prohibited to defile himself even under these circumstances.
A Kohein is prohibited from serving in the Beis HaMikdosh in a state of tumah. Even a person that is not a Kohein must be tahor when entering the Beis HaMikdosh or eating korbanos. The complete separation between the Beis HaMikdosh and tumah requires that even terumah, the holy food of the kohein, and ma'aser sheini, the tithe eaten in Jerusalem, must be preserved in the state of taharah. Why is tumah the antithesis of the Beis HaMikdosh, thereby requiring scrupulous care that anything associated with the Beis HaMikdosh remain tahor?
All forms of tumah are linked to a loss of life. The highest level of tumah is linked to the most profound loss of life, the death of a human being. Dead animals also emit tumah, albeit to a lesser degree. Even the loss of potential life such as when a woman becomes a niddah is associated with tumah.
According to the Ramban in the beginning of Vayikra, the primary purpose of bringing a korban is a reaffirmation of life. One who sins deserves death according to the strict rules of justice. Hashem in His mercy wants us to offer an animal in place of ourselves, thereby reminding us that it is the kindness of Hashem that grants us another opportunity to live.
The Beis HaMikdosh and everything surrounding it represent the gift of renewal of life. Tumah, which is synonymous with death, has no place in the Beis HaMikdosh. The kohein who serves in the Beis HaMikdosh must be a symbol of this renewal and have no association with the loss of life. The message emanating from the Beis HaMikdosh is clear: come back to Hashem, begin your life again, and celebrate this renewal in a state of holiness and taharah.