1 Chronicles 23:9

David organized the Levites into groups based on their family lines. There were more clerics than needed for one temple. These groups allowed all priests and Levites to take turns serving in the temple (see Luke 1:5, 8).

SONS OF GERSHON. (Ch1 23:7-11)

the Gershonites--They had nine fathers' houses, six descended from Laadan, and three from Shimei.

Here we have, I. The crown entailed, according to the divine appointment, Ch1 23:1. David made Solomon king, not to reign with him, or reign under him, but only to reign after him. This he did, 1. When he was old and full of days. He was but seventy years old when he died, and yet he was full of days, satur dierum - satisfied with living in this world. When he found himself going off, he made provision for the welfare of the kingdom after his decease, and pleased himself with the hopeful prospect of a happy settlement both in church and state. 2. He did it in parliament, in a solemn assembly of all the princes of Israel, which made Adonijah's attempt to break in upon Solomon's title and set it aside, notwithstanding this public recognition and establishment of it, the more impudent, impious, and ridiculous. Note, The settling or securing of the crown in the interests of the temple is a great blessing to the people and a great satisfaction to those who are themselves leaving the world.
II. The Levites numbered, according to the rule in Moses's time, from thirty years old to fifty, Num 4:2, Num 4:3. Their number in Moses's time. by this rule, was 8580 (Num 4:47, Num 4:48), but now it had increased above four-fold, much more in proportion than the rest of the tribes; for the serviceable men of Levi's tribe were now 38,000, unless we suppose that here those were reckoned who were above fifty, which was not the case there. Joab had not numbered the Levites (Ch1 21:6), but David now did, not in pride, but for a good purpose, and then he needed not fear wrath for it.
III. The Levites distributed to their respective posts (Ch1 23:4, Ch1 23:5), that every hand might be employed (for, of all men, an idle Levite makes the worst figure), and that every part of the work might be carefully done. Now it was for the honour of God that so great a number of servants attended his house and the business of it. Much of the state of great men consists in the greatness of their retinue. When God kept house in Israel see what a great household he had, and all well fed and well taught. But what were these to the attendants of his throne above, and the innumerable company of angels? It was the happiness of Israel that they had among them such a considerable body of men who were obliged by their office to promote and keep up religion among them. If the worship of God go to decay in Israel, let it not be said that it was for want of due provision for the support of it, but that those who should have done it were careless and false. The work assigned the Levites was four-fold: - 1. Some, and indeed far the greater number, were to set forward the work of the house of the Lord: 24,000, almost two-thirds, were appointed for this service, to attend the priests in killing the sacrifices, flaying them, washing them, cutting them up, burning them, to have the meat-offerings and drink-offerings ready, to carry out dirt, and keep all the vessels and utensils of the temple clean, and every thing in its place, that the service might be performed both with expedition and with exactness. These served 1000 a-week, and so went round in twenty-four courses. Perhaps while the temple was in building some of these were employed to set forward that work, to assist the builders, at least to quicken them, and keep good order among them, and the decorum which became temple-work. 2. Others were officers and judges, not in the affairs of the temple, and in the controversies that arose there (for there, we may suppose, the priests presided), but in the country. They were magistrates, to give the laws of God in charge, to resolves difficulties, and to determine controversies that arose upon them. Of these there were 6000, in the several parts of the kingdom, that assisted the princes and elders of every tribe in the administration of justice. 3. Others were porters, to guard all the avenues of the house of God, to examine those that desired entrance, and to resist those that would force an entrance. These were the life-guards of the temple, and probably were armed accordingly. 4. Others were singers and players on instruments, whose business it was to keep up that part of the service; this was a new-erected office.
IV. The Levites mustered, and disposed of into their respective families and kindreds, that an account of them might the better be kept, and those that neglected their duty might be the more easily discovered, by calling over the roll, and obliging them to answer to their names, which each family might do for itself. When those of the same family were employed together it would engage them to love and assist one another. When Christ sent forth his disciples two and two he put together those that were brethren. Two families were here joined in one (Ch1 23:11) because they had not many sons. Those that are weak and little, separately, may be put together and appear considerable. That which is most observable in this account of the families of the Levites is that the posterity of Moses (that great man) stood upon the level with common Levites, and had no dignities or privileges at all peculiar to them; whilst the posterity of Aaron were advanced to the priest's office, to sanctify the most holy things, Ch1 23:13. It is said indeed of the grandson of Moses, Rehabiah, that his sons were highly multiplied, Ch1 23:17, margin. When God proposed to him that, if he would let fall his intercession for Israel, he would make of him a great nation, he generously refused it, in recompence for which his family is here greatly increased, and makes up in number what it wants in figure, in the tribe of Levi. Now, 1. The levelling of Moses' family with the rest is an evidence of his self-denial. Such an interest had he both with God and man that if he had aimed to raise his own family, to dignify and enrich that, he might easily have done so; but he was no self-seeking man, as appears from his leaving to his children no marks of distinction, which was a sign that he had the spirit of God and not the spirit of the world. 2. The elevation of Aaron's family above the rest was a recompence for his self-denial. When Moses (his younger brother) was made a god to Pharaoh, and he only his prophet or spokesman, to observe his orders and do as he was bidden, Aaron never disputed it, nor insisted upon his seniority, but readily took the inferior post God put him in, submitted to Moses, and, upon occasion, called him his lord; and because he thus submitted himself, in his own person, to his junior, in compliance with the will of God, God highly exalted his family, even above that of Moses himself. Those that are content to stoop are in the fairest way to rise. Before honour is humility.

Four thousand praised the Lord - David made this distribution according to his own judgment, and from the dictates of his piety; but it does not appear that he had any positive Divine authority for such arrangements. As to the instruments of music which he made they are condemned elsewhere; see Amo 6:5, to which this verse is allowed to be the parallel.

The sons of Shimei,.... Not him that was the son of Gershon, but a descendant of Laadan, his son, as Kimchi observes:

Shelomith, and Haziel, and Haran, these were the chief of the fathers of Laadan; of the families that sprang from him.

And the sons of Shimei,.... The son of Gershon, and brother of Laadan, according to Kimchi, which seems right:

were Jahath, Zina, and Jeush, and Beriah; these four were the sons of Shimei; descendants of his in the times of David.