Those who were to camp before the tabernacle on the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, guarding the sanctuary itself, to protect the people of Israel. And any outsider who came near was to be put to death.
The Levites being granted to Aaron to minister to him, they are here delivered to him by tale, that he might know what he had, and employ them accordingly. Observe, I. By what rule they were numbered: Every male from a month old and upward, Num 3:15.
Commenting on Numbers 3:14-39
All that were numbered of the Levites, which Moses and Aaron, numbered at the commandment of the Lord, throughout their families,.... Whence it appears, that Moses was not alone, but Aaron with him, in numbering the Levites, and that by the appointment of the Lord.
those that encamp, &c.--That being the entrance side, it was the post of honor, and consequently reserved to Moses and the priestly family. But the sons of Moses had no station here.