The exact historical relationship between the priests and the Levites seems obscure at times. Originally the priests could only be the direct male descendants of Aaron, the brother of Moses and the first priest. They alone were permitted to offer the sacrifices outlined in the Mosaic Law. The Levites, descendants of Levi, the third son of Jacob and Leah, served as assistants to the priests. They undertook all the manual labor involved in setting up and taking down the tabernacle as it was moved from place to place. In time the Levites became the substitutes for firstborn sons of all other Israelites, who were-like the first-born males of all animals-to be dedicated to God. A fee was paid to the Levite to serve as a substitute, thus releasing the first-born son of non-Levites from life-long religious service.
When the worship of God became centered in the temple, the Levites no longer had the responsibility of moving the tabernacle. Instead they were made assistants to the priests in sanctuary work. They also served as judges, scribes, gatekeepers, and musicians. After the Exile, they helped in the reconstruction of the temple, and became experts in teaching religion to the people. By New Testament times, there was a high ratio of priests to the general population. Some scholars have estimated that 24,000 priests were permanently assigned to Jerusalem, while another 12,000 lived in Jericho. Every priest was assigned to one of twenty-four "courses" or orders, each of which served for a week at a time. Similarly, Levites were divided into twenty-four orders, which served in rotation. Levites lived in a number of "Levitical cities," in which they were given special privileges and property. Both Levites and priests traveled back and forth to Jerusalem from their homes several times a year to attend the festivals and to serve in the temple with their order. The sight of priests and Levites on the road between Jerusalem and Jericho was common; Jesus used that familiar scene to good advantage in his parable of the Good Samaritan.