Rabbi Ishmael said: All firstborns are required to have a tithe taken (only) when they fall under the observation of the eye. Only Jacob observed the law of tithe in advance; he began with Benjamin, who was in his mother's womb, and Levi was reckoned as holy to the Lord, and concerning him the Scripture says, "The tenth shall be holy unto the Lord" (ibid.).
Michael, the angel, descended and took Levi, and brought him up before the Throne of Glory, and he spake before Him: Sovereign of all || the universe! This is Thy lot, and the portion of Thy works. And He put forth His right hand and blessed him, that the sons of Levi should minister on earth before Him, like the ministering angels in heaven. Michael spake before the Holy One, blessed be He: Sovereign of all worlds! Do not such who serve the king have provision of their food given to them? Therefore He gave to the sons of Levi all holy things which accrue to His Name, as it is said, "They shall eat the offerings of the Lord made by fire, and his inheritance" (Deut. 18:1).