Leviticus 13:2

When a man shall have in the skin of his flesh
Rules are here given, by which a leprosy might be judged of; which, as a disease, was frequent in Egypt, where the Israelites had dwelt a long time, and from whence they were just come; and is doubtless the reason, as learned men have observed, that several Heathen writers make the cause of their expulsion from Egypt, as they choose to call it, though wrongly, their being infected with this distemper; whereas it was the reverse, not they, but the Egyptians, were incident to it ^F26. Moreover, the leprosy here spoken of seems not to be the same with that disease, or what we now call so, though some have thought otherwise; it being rather an uncleanness than a disease, and the business of a priest, and not a physician to attend unto; and did not arise from natural causes, but was from the immediate hand of God, and was inflicted on men for their sins, as the cases of Miriam, Gehazi, and Uzziah show; and who by complying with the rites and ceremonies hereafter enjoined, their sins were pardoned, and they were cleansed; so that as their case was extraordinary and supernatural, their cure and cleansing were as remarkable: besides, this impurity being in garments and houses, shows it to be something out of the ordinary way. And this law concerning it did not extend to all men, only to the Israelites, and such as were in connection with them, such as proselytes. It is said ^F1, all are defiled with the plague (of leprosy) except an idolater and a proselyte of the gate; and the commentators say ^F2, even servants, and little ones though but a day old; that is, they are polluted with it, and so come under this law. Now the place where this disorder appears is "in the skin of the flesh"; that is, where there is a skin, and that is seen; for there are some places, the Jewish writers ^F3 say, are not reckoned the skin of the flesh, or where that is not seen, and such places are excepted, and they are these; the inside of the eye, of the ear, and of the nose: wrinkles in the neck, under the pap, and under the arm hole; the sole of the foot, the nail, the head and beard: and this phrase, "in the skin of his flesh", is always particularly mentioned; and when there appeared in it

a rising, scab, or bright spot;
the scab that is placed between the rising or swelling, and the bright spot, belongs to them both, and is a kind of an accessory, or second to each of them: hence the Jews distinguish the scab of the swelling, and the scab of the bright spot; so that these make four in all, as they observe ^F4. And to this agrees what Ben Gersom on this text remarks; the bright spot is, whose whiteness is as the snow; the rising or swelling is what is white, as the pure wool of a lamb of a day old; the scab is what is inferior in whiteness to the rising, and is as in the degree of the whiteness of the shell or film of an egg; and this is the order of these appearances, the most white is the bright spot, after that the rising, and after that the scab of the bright spot, and after that the scab of the rising or swelling; and, lo, what is in whiteness below the whiteness of this (the last) is not the plague of leprosy:

and it be in the skin of his flesh [like] the plague of leprosy;
either of the above appearances in the skin, having somewhat in them similar to the leprosy, or which may justly raise a suspicion of it, though it is not clear and manifest;

then he shall be brought to Aaron the priest, or unto one of his
sons the priests;
for, as Jarchi notes, there was no pollution nor purification of the leprosy, but by the mouth or determination of a priest. And a good man that was desirous, and made conscience of observing the laws of God, when he observed anything of the above in him, and had any suspicion of his case, would of himself go, and show himself to the priest; but if a man did not do this, and any of his neighbours observed the appearances on him, brought him to the priest whether he would or not, according to the text,

he shall be brought:
that is, as Aben Ezra explains it, whether with or without his will; for he that sees in him one of the signs, shall oblige him to come to the priest; and who observes, that by Aaron the priest is meant, the priest anointed in his room; and by his sons the priests, the common priests, who are found without the sanctuary; such as the priests of Anathoth, but who were not of those that were rejected.