From twenty and five years old and upward. — This regulation may be understood as referring to the age at which the Levites were to enter upon their duties after the people had taken possession of the land of Canaan, and it appears to have remained in force until the time of David, who substituted the age of twenty for that of twenty-five, because the necessity of carrying the Tabernacle and its furniture from place to place, which arose but seldom after the entrance into Canaan, finally ceased after the removal of the ark to Mount Zion. The time of service during the wanderings in the wilderness was from thirty to fifty (Numbers 4:3; Numbers 4:23; Numbers 4:30), during which time the constant removal of the Tabernacle required the services of men in the full vigour of life. The chronological order of events is not always observed in this book, and the directions contained in Numbers 8:23-26 may have been given at a later period, but inserted here in connection with the account of the appointment of the Levites to their office. On the other hand, it is quite possible that from the first the Levites entered upon the lighter parts of their office at the age of twenty-five years, but were not employed before they were thirty years of age in the more onerous duties of removing the Tabernacle, or in bearing on their shoulders the sacred vessels, as in the case of the Kohathites.
To wait upon the service. — Literally, to war the warfare, or to serve the (military) service. Similarly, in the following verse, he shall return from the warfare of the service.