Midrash su Levitico 14:55

Rabba b. Huna said: "There is one great preference between an Israelite and a Proselyte. Concerning the Israelite the passage reads (Ez. 37, 27) And I will be their God, and they shall be My people, but concerning a Proselyte it is written (Jer. 30, 21) For who is this that has pledged his heart to approach unto Me?" R.Chelbo said:"Proselytes are as bad to Israel as a sore on the skin; for it is written (Is. 14, 1) And the stranger shall be joined unto them, and they shall attach (V'niss'pechu) themselves to the house of Jacob. It is written here [in the Text] V'niss'pchu, and it is written [concerning leprosy] the same expression (Lev. 14, 56) And for a swelling and for a rising (Sapachath)." R. Chama b. Chanina said: "At the time when the Holy One, praised be He, (Fol. 71) will purify the tribes He will commence with the tribe of Levi first, as it is said (Mal. 3, 3) And He will sit as a melter and purifier of silver; and He will purify the sons of Levi, and refine them as gold and silver, that they may offer unto the Lord an offering in righteousness." R. Joshua b. Levi said: "Impure families who joined Israel through the influence of their wealth, will be purified, as it is said (Mal. 3, 3) And He will sit as a melter and purifier of silver. What does the passage (Ib.) That they may offer unto the Lord an offering in righteousness, mean? Said R. Isaac: "Righteousness has the Lord done with Israel that every family which was mixed up beyond recognition is considered pure."

12) (Vayikra 13:59) ("This is the law of the plague-spot of leprosy, in a garment of wool or linen, or in the warp, or in the woof, or in any article of skin, to declare it clean or to declare it unclean.") "This is the plague-spot of leprosy, etc.": (Vayikra 14:54) ("This is the law for all plague-spots or leprosy and for a nethek (Vayikra 14:55) and for the leprosy of a garment and of a house.") They (plague-spot garments) are being likened to a house, viz., Just as a house is rendered unclean by the entry (of an unclean person), so it is rendered unclean by the entry of all (plague-spot garments). — But perhaps just as a house requires birds (for its cleansing, [viz. Vayikra 14:49]), so all (plague-spot garments) should require birds (for their cleansing)! It is, therefore, written "This" (i.e., only in this respect [that of "entry"] are they similar, and not in the other.) Rebbi says: It is written "This is the law for all plague-spots of leprosy and for a nethek and for the leprosy of a garment and of a house." Just as a house renders unclean by entry, so all are rendered unclean by entry. This tells me only of a garment. Whence do I derive all of them (i.e., warp and woof, etc.) for inclusion? From "This is the law of the plague-spot of leprosy … in the warp or in the woof, etc." Just as a garment renders unclean by entry, so all (i.e., warp and woof, etc.) render unclean by entry. — But perhaps just as a garment is rendered unclean by all that are tamei (e.g., sheratzim, semen, etc.), so all (warp and woof etc.) are rendered unclean by all that are tamei! It is, therefore, written "This" (and not the others).