Could anyone help me with this question? In Numbers 8:24-25, the age limit of the Levites that "wait upon the service" was 25-50; then why in Numbers 4, only those between age 30 to 50 were numbered?"
"Take a census of the sons of Kohath from among the children of Levi, by their families, by their fathers' house, from thirty years old and above, even to fifty years old, all who enter the service to do the work in the tabernacle of meeting" (Numbers 4:2-3).
This was not a numbering of all Levites, but only those of the family Kohath who would be involved in the carrying of the articles of the tabernacle. God only wanted the fully matured males involved in this important and heavy work.
"This is what pertains to the Levites: From twenty-five years old and above one may enter to perform service in the work of the tabernacle of meeting; and at the age of fifty years they must cease performing this work, and shall work no more. They may minister with their brethren in the tabernacle of meeting, to attend to needs, but they themselves shall do no work. Thus you shall do to the Levites regarding their duties" (Numbers 8:24-26).
All Levites, not just the sons of Kohath, were used in the daily work within the tabernacle. The age range for these duties was from 25 to 50.
Later, at the time of the building of the Temple, there was a numbering again of the Levites in the 30 to 50 range: "Now the Levites were numbered from the age of thirty years and above; and the number of individual males was thirty-eight thousand" (I Chronicles 23:3). But David, as God's prophet, changed the age range to 20 to 50.
"These were the sons of Levi by their fathers' houses-the heads of the fathers' houses as they were counted individually by the number of their names, who did the work for the service of the house of the LORD, from the age of twenty years and above. For David said, "The LORD God of Israel has given rest to His people, that they may dwell in Jerusalem forever"; and also to the Levites, "They shall no longer carry the tabernacle, or any of the articles for its service." For by the last words of David the Levites were numbered from twenty years old and above; because their duty was to help the sons of Aaron in the service of the house of the LORD, in the courts and in the chambers, in the purifying of all holy things and the work of the service of the house of God, both with the showbread and the fine flour for the grain offering, with the unleavened cakes and what is baked in the pan, with what is mixed and with all kinds of measures and sizes; to stand every morning to thank and praise the LORD, and likewise at evening; and at every presentation of a burnt offering to the LORD on the Sabbaths and on the New Moons and on the set feasts, by number according to the ordinance governing them, regularly before the LORD; and that they should attend to the needs of the tabernacle of meeting, the needs of the holy place, and the needs of the sons of Aaron their brethren in the work of the house of the LORD" (I Chronicles 23:24-32).
The change was due to two factors: the Temple was in a fixed location, so there no longer was a need for men to carefully carry the furnishings. Plus the Temple service was greater and needed more men.