Numbers 4:3

From thirty years old and upward even until fifty years old. — The previous census of the Levites was from a month old. The present census was with a view to the discharge of duties requiring a considerable amount of physical strength, and hence the prescribed age for entering upon these duties was fixed at this time at thirty, and limited to fifty. It has been supposed by some that five years were spent in preparation for the service, and that it is in this way that the apparent discrepancy between this verse and Numbers 8:24, where the age for entering upon the service is fixed at twenty-five, is to be reconciled. (See Note on Numbers 8:24.) In Eastern countries the strength fails at an earlier period than in colder and more temperate climates. Thirty was the age at which John the Baptist and our Lord entered upon their public ministry.

All that enter into the host. — Or, every one who enters upon the service. The word zaba, commonly rendered host, and used elsewhere to denote military service, is here used to denote the service of the sanctuary.