He did not say: do not do foolish things, but: do not even touch them. Uncleanness is of two kinds: bodily and spiritual. To the spiritual belong impure thoughts, impure gazes, malice, deceit, and the like; while to bodily uncleanness belong: fornication, adultery, and every indulgence of the flesh. So then, he wants us to be clean from both the one and the other uncleanness. "Come out from the midst" of the unbelievers "and be separate," that is, live apart and be clean, and then I will receive you. For when you depart from vices, then you will be united with God.
2 Cor. 6:18. And I will be a Father to you, and you shall be My sons and daughters, says the Lord Almighty.
Do you see how the prophet long ago foretold the present regeneration and adoption that is accomplished in us through baptism?