It has been questioned whether the number of the first-born, which is 22,273, can in any way be made to agree with the total number of the male Israelites, previously stated at 603,550. Wellhausen is specially contemptuous of a tradition or calculation which, he says, would give an average of forty children to each woman. But the difficulty partly yields if it is kept in view that the Levites were separated for the service of the sanctuary. Naturally it would be the heir-apparent alone of each family group whose liability to this kind of duty fell to be considered. The head of a household was, according to the ancient reckoning, its priest. In Abraham's family no one counted as a first-born but Isaac. Now that a generation of Israelites is growing up sanctified by the covenant, it appears fit that the presumptive priest should either be devoted to sacerdotal duty, or relieved of it by a Levite as his substitute. Suppose each family had five tents, and suppose further that the children born before the exodus are not reckoned, the number will not be found at all disproportionate. The absolute number remains a difficulty. Dr. Robertson Smith argues from his own premises about the sanctity of the first-born. He repudiates the notion that at one time the Hebrews actually sacrificed all their first-born sons; yet he affirms that "there must have been some point of attachment in ancient custom for the belief that the Deity asked for such a sacrifice."[1] "I apprehend," he proceeds, "that all the prerogatives of the first-born among Semitic peoples are originally prerogatives of sanctity; the sacred blood of the kin flows purest and strongest in him (Gen. xlix. 3). Neither in the case of children nor in that of cattle did the congenital holiness of the first-born originally imply that they must be sacrificed or given to the Deity on the altar, but only that if sacrifice was to be made, they were the best and fittest because the holiest victims." The passage in Numbers may be confidently declared to be far from any such conception. The special fitness for sacrifice of the first-born of an animal is assumed: the fitness of the heir of a family, again, is plainly not to _become_ a sacrifice, but to offer sacrifice. The first-born of the Egyptians died. But it is the life, the holy activity of His own people, not their death, God desires. And this holy activity, rising to its highest function in the first-born, is according to our passage laid on the Levites to a certain extent. Not entirely indeed. The whole congregation is still consecrated and must be holy. All are bound by the covenant. The head of each family group will still have to officiate as a priest in celebrating the passover. Certain duties, however, are transferred for the better protection of the sanctities of worship.