The great and awesome levitical and aaronic priesthood began when Moses wrote of the following,

Thus Moses and Aaron and all the congregation of the children of Israel did to the Levites; according to all that the Lord commanded Moses concerning the Levites, so the children of Israel did to them. And the Levites purified themselves and washed their clothes; then Aaron presented them like a wave offering before the Lord, and Aaron made atonement for them to cleanse them. After that the Levites went in to do their work in the tabernacle of meeting before Aaron and his sons; as the Lord commanded Moses concerning the Levites, so they did to them (Numbers 8:20–22).

For fifteen hundred years that priesthood lasted, all the while foreshadowing a greater priesthood, of which all Christians have a part under the high priesthood of Jesus Christ.