To serve as a Levite, one had to be between thirty and fifty years old (vv. 3, 23, 30, 35, 43, 47). Likewise, the Lord Jesus did not reach the full age for God’s service until He was thirty (Luke 3:23). To be counted in the service to God, one had to be one month old and above — those at that age needed to grow and mature (Num. 3:39, 43). To be counted in the warfare for God’s testimony, one had to be twenty years old or above — those at that age were mature and strong, without limit (1:3). To be counted in the service that was close to God, one had to be between thirty and fifty years old — those at that age were more mature and were stronger, without deterioration.