Adam Clarke on 2 Corinthians 6:17

Wherefore come out from among them - Is it not plain from this and the following verse that God would be their God only on the ground of their taking him for such, and that this depended on their being separated from the works and workers of iniquity? for God could not inhabit in them if they had concord with Belial, a portion with infidels; etc. Those who will have the promises of God fulfilled to them must come under the conditions of these promises: if they are not separate - if they touch the unclean thing, God will not receive them; and therefore will not be their God, nor shall they be his people.