Numbers 7-8
So Moses took the carts and oxen and gave them to the Levites. He gave two carts and four oxen to the Gershonites, as their work required, and he gave four carts and eight oxen to the Merarites, as their work required. They were all under the direction of Ithamar son of Aaron, the priest. But Moses did not give any to the Kohathites, because they were to carry on their shoulders the holy things, for which they were responsible.
When the altar was anointed, the leaders brought their offerings for its dedication and presented them before the altar. For the Lord had said to Moses, “Each day one leader is to bring his offering for the dedication of the altar.”
The one who brought his offering on the first day was Nahshon son of Amminadab of the tribe of Judah.
On the second day Nethanel son of Zuar, the leader of Issachar, brought his offering.
On the third day, Eliab son of Helon, the leader of the people of Zebulun, brought his offering.
On the fourth day Elizur son of Shedeur, the leader of the people of Reuben, brought his offering.
On the fifth day Shelumiel son of Zurishaddai, the leader of the people of Simeon, brought his offering.
On the sixth day Eliasaph son of Deuel, the leader of the people of Gad, brought his offering.
On the seventh day Elishama son of Ammihud, the leader of the people of Ephraim, brought his offering.
On the eighth day Gamaliel son of Pedahzur, the leader of the people of Manasseh, brought his offering.
On the ninth day Abidan son of Gideoni, the leader of the people of Benjamin, brought his offering.
On the tenth day Ahiezer son of Ammishaddai, the leader of the people of Dan, brought his offering.
On the eleventh day Pagiel son of Okran, the leader of the people of Asher, brought his offering.
On the twelfth day Ahira son of Enan, the leader of the people of Naphtali, brought his offering.
The Lord said to Moses, “Speak to Aaron and say to him, ‘When you set up the lamps, see that all seven light up the area in front of the lampstand.’”
The Lord said to Moses: “Take the Levites from among all the Israelites and make them ceremonially clean.
The Lord said to Moses, “This applies to the Levites: Men twenty-five years old or more shall come to take part in the work at the tent of meeting, but at the age of fifty, they must retire from their regular service and work no longer.
25~50 years is the best time in our lives to serve the Lord.
How?
To serve the Lord requires some qualities; they are the chosen ones.