In | Sacred Personnel

It may be surprising to learn that all priests were Levites, but not all Levites were priests. The terms are not interchangeable. Levites were descendants of Levi, one of the 12 sons of Jacob. Only descendants of Aaron, himself a Levite, were priests. Still confused? This should help. 

The Levites were in charge of virtually everything that had to do with the Tabernacle and later on the Temple: the music, the furniture and all the rituals. The roles of different Levites varied according to their ancestry. For example, the Kohathites carried the furniture of the Tabernacle from one site to another; the Gershonites carried the curtains of the Tabernacle and courtyard, while only the sons of Aaron performed priestly duties.