What is this Pasuk coming to tell us?
Rashi #1: 'Do not render the land Tamei, 1 thereby forcing Me to dwell in the land when it is Tamei, since Hashem's Shechinah rests in Yisrael even when they are Tamei'.
Rashi #2 (in Yoma, 85a): That a. murder is a terrible sin that contaminates the ;and, and b. If one contaminates the land, the Shechinah will not rest in it.
Ha'amek Davar: The Shechinah cannot be in a Tamei place. If we are Metamei the land 2 , since the Shechinah dwells among Yisrael, this obligates exile of Yisrael.