"you will, in the end, partake of their uncleanliness." this double language of "do not soil" and "you will become unclean" seems extra if you say "do not soil yourselves" so it's obvious that if you eat you will becomes unclean- but the Torah is hinting through this double language, "do not soil yourselves with them.." because if you start to soil yourselves- you will eventually partake in their impurity - meaning it will envelope you in a covering of impurity that is sealed off more so than how you thought it will end if you soil yourselves with them, you will, in the end, partake of their uncleanliness." 