Why must believers be separated from unbelievers?
Separation is required because God forbids being unequally yoked with unbelievers, and it preserves the spiritual distinction and power He intends. Just as He separated Israel from Egypt, He wants believers separated from the world, so the world can see where His people stand.
Les explains that Paul commands believers not to be unequally yoked together with unbelievers, asking what concord or relationship a believer has with an infidel. Les teaches that separation is seldom mentioned today, and he maintains this is exactly why Christianity has lost its power: the average person cannot see any difference between the average Christian and the average person of the world. God did not intend that. Just as surely as He separated Israel from Egypt, He wants to separate believers from the world. This does not mean believers are to be oddballs or constantly ask for persecution by their actions, but the world should know where they stand. Therefore, all the way through, believers have to be separated.
And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?