In keeping with the chronicler's priestly interest, much emphasis is placed upon the organization of the Temple and temple worship. A thorough knowledge of it was important for the re-establishment of temple worship after the return from the Exile under the leadership of Ezra, the most likely author of Chronicles.
After David had made the arrangements for the building of the Lord's House (chapter 22), he focussed his energies on organizing the priests and Levites. The first step was to number them "from the age of thirty years and above" (23:3), probably until age fifty (cf. Numbers 4:3). The age of thirty was considered one of full maturity and worthy of respect. Jesus was thirty years old when He began His full-time ministry. David later lowered the required age limit to twenty (23:24, 27), possibly to include more men in the work force because of the greater demands of the large centralized place of worship in Jerusalem; or possibly, twenty was the age of enlistment which was then followed by some years of training or apprenticeship before they took on full responsibilities at the age of thirty.
The Levites were divided into four operational groups. The largest group of 24,000 was to work in various capacities directly involved in the service of the House of God. 6,000 were to be judges and officials, representing God and the king throughout Israel (cf. 26:29-32). 4,000 were to be gatekeepers, including the trusted keepers of the treasury, and another 4,000 were to minister unto the Lord and the people in song. David himself was not only a gifted musician, but an inventor of musical instruments for the glory of God. His instruments were used by the Temple musicians for praising God (23:5; cf. Amos 6:5). These four groups were then further divided by David into 24 groups which were assigned by lot to serve at the House of the Lord on a rotation basis.
David was an administrative genius. His organization of Levit-ical ministry was a significant accomplishment and a great contribution for posterity. David's system was even intact in New Testament times. Zacharias, John the Baptist's father, was a priest of the division of Abijah (24:10; Luke 1:5). David's motivation was to ensure the continuation of true worship to God in the House of the Lord — in praise to Him (23:5), in ministering to Him, and in blessing the people in His Name (23:13). The Levites' main responsibilities were to help the priests in service to God, attend to every need (23:28, 32), and continually give thanks and praise to the Lord, especially at those two very important times of the day, morning and evening, when the daily sacrifices were offered (23:30-31); Exodus 29:38-39).
The priest's role of offering sacrifices unto the Lord in Israel continued to be valid until the time of Jesus Christ's great, perfect, and final sacrifice of Himself. Henceforth, there was no need for the sacrifices of the Temple; yet several of the other responsibilities of the priests and Levites remain. We, as believers in Jesus, are now His royal priesthood (1 Peter 2:9). It is our duty to worship Him in spirit and in truth, and we are to daily give praise and thanks to him. Romans 12:1 does, however, exhort us to offer a sacrifice to God — our bodies as a "living sacrifice, holy and acceptable unto Him."