We Must Separate Ourselves From Those Who Reject The Atonement Of Jesus Christ

Give orders to the children of Israel to put outside the tent-circle every leper, and anyone who has any sort of flow from his body, and anyone who is unclean from the touch of the dead;
Numbers 5:2

We must separate ourselves from those who reject Jesus Christ as the head of The Church in all things.
They have a morally polluted mind, because they have let sin reign in it, and must be separated out of our midst.