Numbers Chapter 3
The Levites, with their assigned levels of responsibility, were given to attend to the center of worship, all of the things that were living symbols of the coming Messiah (see What Is Jesus Christ Doing Right Now?).
"These are the generations of Aaron and Moses [see The Education Of Moses; also The Trysting Tent and Why Did Christ Put Moses To Death?] at the time when The Lord spoke with Moses on Mount Sinai.
These are the names of the sons of Aaron: Nadab the first-born, and Abihu, Eleazar, and Ithamar; these are the names of the sons of Aaron, the anointed priests, whom he ordained to minister in the priest's office. But Nadab and Abihu died before The Lord when they offered unholy fire before The Lord in the wilderness of Sinai [see also The Wilderness of Sin]; and they had no children. So Eleazar and Ithamar served as priests in the lifetime of Aaron their father."
And The Lord said to Moses, "Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister to him. They shall perform duties for him and for the whole congregation before the tent of meeting, as they minister at The Tabernacle; they shall have charge of all the furnishings of the tent of meeting, and attend to the duties for the people of Israel as they minister at the tabernacle. And you shall give the Levites to Aaron and his sons; they are wholly given to him from among the people of Israel. And you shall appoint Aaron and his sons, and they shall attend to their priesthood; but if any one else comes near, he shall be put to death." (Numbers 3:1-10 RSV)
Even the order of the camp had a symbolic purpose toward the coming Messiah (see Why Did They Face East?).
"And those to encamp before the tabernacle on the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, having charge of the rites within the Sanctuary, whatever had to be done for the people of Israel; and any one else who came near was to be put to death." (Numbers 3:38 RSV)
Numbers Chapter 4
Specific Levites had specific duties. After the deaths of Nadab and Abihu, all well understood that there was only one proper way to worship The Lord - the way that He commanded, each within their own areas of responsibility (see The Fact Finder question below).
"And when Aaron and his sons have finished covering the sanctuary and all the furnishings of the sanctuary, as the camp sets out, after that the sons of Kohath shall come to carry these, but they must not touch the holy things, lest they die. These are the things of the tent of meeting which the sons of Kohath are to carry.
"And Eleazar the son of Aaron the priest shall have charge of the oil for the light, the fragrant incense, the continual cereal offering, and the anointing oil, with the oversight of all the tabernacle and all that is in it, of the sanctuary and its vessels."
The Lord said to Moses and Aaron, "Let not the tribe of the families of the Kohathites be destroyed from among the Levites; but deal thus with them, that they may live and not die when they come near to the most holy things: Aaron and his sons shall go in and appoint them each to his task and to his burden, but they shall not go in to look upon the holy things even for a moment, lest they die." (Numbers 4:15-20 RSV)
"This is the service of the families of the Gershonites, in serving and bearing burdens: they shall carry the curtains of the tabernacle, and the tent of meeting with its covering, and the covering of goatskin that is on top of it, and the screen for the door of the tent of meeting, and the hangings of the court, and the screen for the entrance of the gate of the court which is around the tabernacle and the altar, and their cords, and all the equipment for their service; and they shall do all that needs to be done with regard to them." (Numbers 4:24-26 RSV)
Numbers Chapter 5
As with the laws for a healthy diet (see Clean and Unclean), The Lord instructed the Israelites in proper health and hygiene within their very large population in The Camp i.e. the census counted over 600,000 military-age Israelites alone (Numbers 2:32).
"The Lord said to Moses, "Command the people of Israel that they put out of the camp every leper, and every one having a discharge, and every one that is unclean through contact with the dead; you shall put out both male and female, putting them outside the camp, that they may not defile their camp, in the midst of which I dwell." And the people of Israel did so, and drove them outside the camp; as The Lord said to Moses, so the people of Israel did." (Numbers 5:1-4 RSV)
Fact Finder: How was the Levitical high priesthood conducted until the time of the coming of the High Priest that they merely symbolized?
See The Lines Of Eleazar and Ithamar