Midrasch zu Wajikra 13:1

1) "And He called to Moses and the L–rd spoke to him, etc." "to him" — to exclude Aaron. R. Yehudah b. Betheira said: Thirteen dibroth (accompanied by a command) were stated in the Torah to Moses and Aaron, and, corresponding to them, thirteen limitations, to teach us that they were not spoken to Aaron, but to Moses, to tell them to Aaron. (The dibroth: 1) [Shemoth 6:13]; 2) [Shemoth 7:8]; 3) [Shemoth 9:8]; 4) [Shemoth 12:1]; 5) [Shemoth 12:43]; 6) [Vayikra 11:1]; 7) [Vayikra 13:1]; 8) [Vayikra 14:33]; 9 [Vayikra 15:1]; 10 [Bamidbar 2:1]; 11 [Bamidbar 4:1]; 12 [Bamidbar 4:18]; 13) [Bamidbar 19:2].)

1) (Vayikra 13:1) ("And the L–rd spoke to Moses and to Aaron, saying: (Vayikra 13:2) A man, if there shall be in the skin of his flesh se'eth or sapachath or bahereth, and it become in the skin of his flesh a plague-spot of leprosy, then he shall be brought to Aaron the Cohein or to one of his sons, the Cohanim.") "if there shall be in the skin of his flesh": What is the intent of this ("shall be" rather than "is")? Because it is written (Vayikra 13:38) "And a man or a woman, if there be in the skin of their flesh white beharoth … he is clean," this tells me only of beharoth which did not arrive at the status of maroth ("appearances" [of plague-spots]) viz.: plague-spots (negaim) which appeared in a non-Jew before he became a proselyte (even though it remained the same after his conversion; (a plague-spot) in a fetus before it was born (which could not be inspected by the Cohein in utero, and which remained the same after birth); in a crease (in the flesh) which was (later) revealed (when the flesh became taut); in the head and the beard (which appeared when he became bald); in a "rebellious" boil or burn or inflammation — (All of these are clean even though they are now "maroth," because when they originated they were not susceptible of inspection by the Cohein. What is their status) if their appearance changes, either lessening or deepening in intensity? R. Elazar b. Azaryah says: It is clean, (for though it changed in appearance, it still originated from the first, non-inspectable plague-spot). R. Elazar b. Chasma says: If of lesser intensity, it is clean (being a "waning" of the original plague-spot); if of deeper intensity, it is to be inspected anew, (being considered a new plague-spot). R. Akiva says: Whether of lesser or deeper intensity it is to be inspected anew. (And) it is in this connection that it is written "A man, if there shall be" (connoting a change [i.e., deeper or lesser intensity] from a pre-existing condition).

2) "if there shall be": from this pronouncement on, (and not what may have existed before it, (their being in this respect like a proselyte before conversion [see above]). — (Why is a verse necessary for this?) Does it not follow? viz.: Zavim (those with a genital discharge) are tamei, and (those with) negaim are tamei. Just as (tumah) does not obtain with zavim before the pronouncement, so, it does not obtain with negaim before the pronouncement.