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.

Reply Obj. 5:  As stated above (ad 4), there was a twofold uncleanness in the Law; one by way of corruption in the mind or in the body; and this was the graver uncleanness; the other was by mere contact with an unclean thing, and this was less grave, and was more easily expiated.  Because the former uncleanness was expiated by sacrifices for sins, since all corruption is due to sin, and signifies sin:  whereas the latter uncleanness was expiated by the mere sprinkling of a certain water, of which water we read in Num. 19.  For there God commanded them to take a red cow in memory of the sin they had committed in worshipping a calf.  And a cow is mentioned rather than a calf, because it was thus that the Lord was wont to designate the synagogue, according to Osee 4:16:  “Israel hath gone astray like a wanton heifer”:  and this was, perhaps, because they worshipped heifers after the custom of Egypt, according to Osee 10:5:  “(They) have worshipped the kine of Bethaven.”  And in detestation of the sin of idolatry it was sacrificed outside the camp; in fact, whenever sacrifice was offered up in expiation of the multitude of sins, it was all burnt outside the camp.  Moreover, in order to show that this sacrifice cleansed the people from all their sins, “the priest” dipped “his finger in her blood,” and sprinkled “it