Unclean - i. e. unholy because the sanctuary was not in it, but on the other side of Jordan.
Related Commentaries of Joshua 22:19
Joshua 22:19
19 Notwithstanding, if the land of your possession be unclean, then pass ye over unto the land of the possession of the LORD, wherein the LORD'S tabernacle dwelleth, and take possession among us: but rebel not against the LORD, nor rebel against us, in building you an altar beside the altar of the LORD our God.