All the firstborn of Israel, who belonged to God, were numbered from birth (3:13). Furthermore, every male of the Levites, who served the tabernacle, was numbered from one month old and above (3:15).
For a vow to God, an Israelite male of the highest valuation was required to be between twenty years old and sixty years old (Lev. 27:3). But for fighting, an Israelite male was required to be twenty years old or above, without limit. Even at the age of eighty-five, Caleb was still a warrior, able to fight for the nation of Israel (Josh. 14:10-11).
The numbering of Israel was recognized by the authorities in three aspects: first, by Moses, signifying Christ as the Head exercising His authority; second, by Aaron, signifying Christ as the High Priest carrying out His priesthood; and third, by the leaders of the twelve tribes, signifying the elders of the churches taking the lead among God's people. If we say that there is no leadership in the church, we annul, put aside, the elders, who are the real and actual leadership in the church life. The church would then become an anarchy; it would be lawless, altogether without government.
The Levites were not numbered among the army (Num. 1:47-54; 2:33). They were appointed to minister to the tabernacle of the testimony and encamp around it to keep it from being touched by the children of Israel.
The fighting Israelites were the outward protection for the serving Levites, who were for the testimony of God. The Levites were encamped around the tabernacle, and they were surrounded by the twelve tribes, who protected them.
The formed Israelites were a type of the church. Ephesians, a book on the church, reveals that the church is a corporate warrior fighting the battle for God's testimony (Eph. 6:10-20). The church is also composed of God's serving ones as the Levites. For fighting, we are a corporate warrior, and for serving we are the Levites, even the priests.