And the Lord spake unto Moses and unto Aaron,.... Aaron is addressed again, though left out in the preceding law, because the laws concerning leprosy chiefly concerned the priests, whose business it was to judge of it, and cleanse from it; and so Ben Gersom observes, mention is made of Aaron here, because to him and his sons belonged the affair of leprosies, to pronounce unclean or clean, to shut up or set free, and, as Aben Ezra says, according to his determination were all the plagues or strokes of a man, who should be declared clean or unclean:
saying; as follows.

The plague of leprosy was an uncleanness, rather than a disease. Christ is said to cleanse lepers, not to cure them. Common as the leprosy was among the Hebrews, during and after their residence in Egypt, we have no reason to believe that it was known among them before. Their distressed state and employment in that land must have rendered them liable to disease. But it was a plague often inflicted immediately by the hand of God. Miriam's leprosy, and Gehazi's, and king Uzziah's, were punishments of particular sins; no marvel there was care taken to distinguish it from a common distemper. The judgment of it was referred to the priests. And it was a figure of the moral pollutions of men's minds by sin, which is the leprosy of the soul, defiling to the conscience, and from which Christ alone can cleanse. The priest could only convict the leper, (by the law is the knowledge of sin,) but Christ can cure the sinner, he can take away sin. It is a work of great importance, but of great difficulty, to judge of our spiritual state. We all have cause to suspect ourselves, being conscious of sores and spots; but whether clean or unclean is the question. As there were certain marks by which to know it was leprosy, so there are marks of such as are in the gall of bitterness. The priest must take time in making his judgment. This teaches all, both ministers and people, not to be hasty in censures, nor to judge anything before the time. If some men's sins go before unto judgment, the sins of others follow after, and so do men's good works. If the person suspected were found to be clean, yet he must wash his clothes, because there had been ground for the suspicion. We have need to be washed in the blood of Christ from our spots, though not leprosy spots; for who can say, I am pure from sin?

Leprosy. - The law for leprosy, the observance of which is urged upon the people again in Deuteronomy 24:8-9, treats, in the first place, of leprosy in men: (a) in its dangerous forms when appearing either on the skin (vv. 2-28), or on the head and beard (Leviticus 13:29-37); (b) in harmless forms (Leviticus 13:38 and Leviticus 13:39); and (c) when appearing on a bald head (Leviticus 13:40-44). To this there are added instructions for the removal of the leper from the society of other men (Leviticus 13:45 and Leviticus 13:46). It treats, secondly, of leprosy in linen, woollen, and leather articles, and the way to treat them (Leviticus 13:47-59); thirdly, of the purification of persons recovered from leprosy (Leviticus 14:1-32); and fourthly, of leprosy in houses and the way to remove it (vv. 33-53). - The laws for leprosy in man relate exclusively to the so-called white leprosy, λεύκη λέπρα, lepra, which probably existed at that time in hither Asia alone, not only among the Israelites and Jews (Numbers 12:10.; 2-Samuel 3:29; 2-Kings 5:27; 2-Kings 7:3; 2-Kings 15:5; Matthew 8:2-3; Matthew 10:8; Matthew 11:5; Matthew 26:6, etc.), but also among the Syrians (2-Kings 5:1.), and which is still found in that part of the world, most frequently in the countries of the Lebanon and Jordan and in the neighbourhood of Damascus, in which city there are three hospitals for lepers (Seetzen, pp. 277, 278), and occasionally in Arabia (Niebuhr, Arab. pp. 135ff.) and Egypt; though at the present time the pimply leprosy, lepra tuberosa s. articulorum (the leprosy of the joints), is more prevalent in the East, and frequently occurs in Egypt in the lower extremities in the form of elephantiasis. Of the white leprosy (called Lepra Mosaica), which is still met with in Arabia sometimes, where it is called Baras, Trusen gives the following description: "Very frequently, even for years before the actual outbreak of the disease itself, white, yellowish spots are seen lying deep in the skin, particularly on the genitals, in the face, on the forehead, or in the joints. They are without feeling, and sometimes cause the hair to assume the same colour as the spots. These spots afterwards pierce through the cellular tissue, and reach the muscles and bones. The hair becomes white and woolly, and at length falls off; hard gelatinous swellings are formed in the cellular tissue; the skin gets hard, rough, and seamy, lymph exudes from it, and forms large scabs, which fall off from time to time, and under these there are often offensive running sores. The nails then swell, curl up, and fall off; entropium is formed, with bleeding gums, the nose stopped up, and a considerable flow of saliva... The senses become dull, the patient gets thin and weak, colliquative diarrhea sets in, and incessant thirst and burning fever terminate his sufferings" (Krankheiten d. alten Hebr. p. 165).