What is the meaning of "Im Temei'ah Eretz Achuzaschem"?
Rashi: Hashem did not choose to rest His Shechinah there.
Radak: If you consider it Tamei because the Mishkan is not there.
Ramban (Bamidbar 21:21): It is not proper for the Beis ha'Mikdash or for the Shechinah to dwell there.
Malbim: If you will say that you built the Mizbe'ach west of the Yarden to offer to Hashem, because is not proper to offer in your land, also this is a rebellion (a) against Hashem, who commanded not to offer on a Bamah, only in the Mishkan, and (b) against Yisrael, for it divides their unity. It is proper that all of Yisrael serve Hashem in one house!
What is the meaning of "v'Osanu Al Timrodu"?
Rashi: It is like "u'Vanu Al Timrodu" (do not rebel against us). Radak