Numbers 3:9
And thou shalt give the Levites unto Aaron and to his sons: they are wholly given unto him out of the children of Israel. And thou shalt give the Levites unto Aaron and to his sons: they are wholly given unto him out of the children of Israel.
The Levites were wholly given to Aaron and to his sons for sacred service in the tabernacle under their direction. The priestly office itself belonged to Aaron's house alone and was distinct from the Levitical service performed under them. The assignment shows that the work of the tabernacle was committed by God to appointed persons and was not left for any tribe or person to take up at will.
Their assigned work was to erect the tabernacle and encamp around it to guard it while the hosts of Israel pitched at a distance. When Israel journeyed they were to take it down and carry it with the ark, the candlestick, and the other sacred articles of furniture. This service was an honor given to the Levites because they took no part in making and worshiping the golden calf and faithfully carried out God's order against the idolaters.
Korah was a Levite appointed to this tabernacle service but became dissatisfied with his position and aspired to the priesthood, so that the distinction between Levitical service and priestly authority became a source of jealousy. Because they had been thus honored, the Levites became ambitious for still higher office and greater influence with the congregation. With Korah, Dathan, Abiram, and two hundred and fifty men of renown they sought to obtain the priesthood and the government in rebellion against Moses and Aaron.
In a later time, Elkanah as a Levite remained especially devoted to the tabernacle service. He had no regular employment there because worship at Shiloh had become irregular and incomplete.