HKB
uncleanness arising from consent in another's sin, according to 2 Cor. 6:17: "Go out from among them, and be ye separate . . . and touch not the unclean thing."
Moreover, this uncleanness arising from the touch was contracted even by inanimate objects; for whatever was touched in any way by an unclean man, became itself unclean. Wherein the Law attenuated the superstition of the Gentiles, who held that uncleanness was contracted not only by touch, but also by speech or looks, as Rabbi Moses states (Doct. Perplex. iii) of a woman in her periods. The mystical sense of this was that "to God the wicked and his wickedness are hateful alike" (Wis. 14:9).
There was also an uncleanness of inanimate things considered in themselves, such as the uncleanness of leprosy in a house or in clothes. For just as leprosy occurs in men through a corrupt humor causing putrefaction and corruption in the flesh; so, too, through some corruption and excess of humidity or dryness, there arises sometimes a kind of corruption in the stones with which a house is built, or in clothes. Hence the Law called this corruption by the name of leprosy, whereby a house or a garment was deemed to be unclean: both because all corruption savored of uncleanness, as stated above, and because the Gentiles worshipped their household gods as a preservative against this corruption. Hence the Law prescribed such houses, where this kind of corruption was of a lasting nature, to be destroyed; and such garments to be burnt, in order to avoid all occasion of idolatry. There was also an uncleanness of vessels, of which it is written (Num. 19:15): "The vessel that hath no cover, and binding over it, shall be unclean." The cause of this uncleanness was that anything unclean might easily drop into such vessels, so as to render them unclean. Moreover, this command aimed at the prevention of idolatry. For idolaters believed that if mice, lizards, or the like, which they used to sacrifice to the idols, fell into the vessels or into the water, these became more pleasing to the gods. Even now some women let down uncovered vessels in honor of the nocturnal deities which they call "Janae."
The figurative reason of these uncleannesses is that the leprosy of a house signified the uncleanness of the assembly of heretics; the leprosy of a linen garment signified an evil life arising from bitterness of mind; the leprosy of a woolen garment denoted the wickedness of flatterers; leprosy in the warp signified the vices of the soul; leprosy on the woof denoted sins of the flesh, for as the warp is in the woof, so is the soul in the body. The vessel that has neither cover nor binding, betokens a man who lacks the veil of taciturnity, and who is unrestrained by any severity of discipline.