We are not to suppose that this legislation has descended to us from the age of Moses without addition and change. Such a belief would be contrary to the history of other religious law-books, or indeed to historical probability. As the utterances of the Hebrew prophets were modified or enlarged according to the circumstances of the successive ages to which they were applied, so too the Mosaic legislation must have undergone revision and enlargement. Laws and regulations which suited the life in the desert needed adaptation to the changed conditions of life in Canaan; tribes fresh from their servitude in Egypt required different guidance from that required by a nation of conquerors; and the details of a legislation which was adapted to the period of Moses would have been wholly unsuited to the period of the Judges, and still more to the period of the Kings. So far as the change and modifications are concerned, which all institutions in this world must necessarily undergo, the Mosaic legislation was a matter of growth. But it was the form and details that changed, not the substance of the legislation. The spirit and conceptions of the legislator had imprinted themselves too indelibly upon it ever to be obliterated. The reiteration of the same law in various forms, and the confused arrangement of many of them, may indeed show that later hands have been at work, but in essence and origin they remain his. The book of Leviticus, modernised though it may be, nevertheless goes back to the age of Moses. Even in the age of Moses many of its regulations were not new. We find their parallels in Babylonia and Canaan, and they had doubtless long been among the unwritten institutions of Israel. But Moses gave them a new sanction and a new adaptation. The Israelites must have had priests like the nations round about them; but it was Moses who defined the priestly character of the sons of Aaron, and consecrated his own tribe to the service of Yahveh. If Yahveh was the national God of Israel, He was also in a special way the tribal God of Levi. We still know too little about the details of Babylonian ritual to be able to compare it with the religious institutions of Israel. We know, however, that the peace-offerings and trespass-offerings of the Mosaic Law were represented in it, that even the heave-offerings found in it their counterpart, and that solemn fasts and days of atonement were observed in Babylonia and Assyria as well as among the Israelites. In Babylonia, too, a distinction was made between clean and unclean animals, and, as in Israel (Lev. xxi. 17-23), none who was maimed or diseased was allowed to minister to the gods. Purification with water, moreover, played much the same part in Babylonian ritual that it played in the ritual of the Israelites, and tithes were exacted for the support of the service in the temples.