A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
1 Chronicles 27:1
ch1 27:1TWELVE CAPTAINS FOR EVERY MONTH. (Ch1 27:1-15)
came in and went out month by month--Here is an account of the standing military force of Israel. A militia formed, it would seem, at the beginning of David's reign (see Ch1 27:7) was raised in the following order: Twelve legions, corresponding to the number of tribes, were enlisted in the king's service. Each legion comprised a body of twenty-four thousand men, whose term of service was a month in rotation, and who were stationed either at Jerusalem or in any other place where they might be required. There was thus always a force sufficient for the ordinary purposes of state, as well as for resisting sudden attacks or popular tumults; and when extraordinary emergencies demanded a larger force, the whole standing army could easily be called to arms, amounting to two hundred eighty-eight thousand, or to three hundred thousand, including the twelve thousand officers that naturally attended on the twelve princes (Ch1 27:16-24). Such a military establishment would be burdensome neither to the country nor to the royal treasury; for attendance on this duty being a mark of honor and distinction, the expense of maintenance would be borne probably by the militiaman himself, or furnished out of the common fund of his tribe. Nor would the brief period of actual service produce any derangement of the usual course of affairs; for, on the expiry of the term, every soldier returned to the pursuits and duties of private life during the other eleven months of the year. Whether the same individuals were always enrolled, cannot be determined. The probability is, that provided the requisite number was furnished, no stricter scrutiny would be made. A change of men might, to a certain degree, be encouraged, as it was a part of David's policy to train all his subjects to skill in arms; and to have made the enlistment fall always on the same individuals would have defeated that purpose. To have confined each month's levy rigidly within the limits of one tribe might have fallen hard upon those tribes which were weak and small. The rotation system being established, each division knew its own month, as well as the name of the commander under whom it was to serve. These commanders are styled, "the chief fathers," that is, the hereditary heads of tribes who, like chieftains of clans, possessed great power and influence.
captains of thousands and hundreds--The legions of twenty-four thousand were divided into regiments of one thousand, and these again into companies of a hundred men, under the direction of their respective subalterns, there being, of course, twenty-four captains of thousands, and two hundred forty centurions.
and their officers--the Shoterim, who in the army performed the duty of the commissariat, keeping the muster-roll, &c.
1 Chronicles 27:2
ch1 27:2Jashobeam the son of Zabdiel--(See on Ch1 11:11; Sa2 23:8). Hachmoni was his father, Zabdiel probably one of his ancestors; or there might be different names of the same individual. In the rotation of the military courses, the dignity of precedence, not of authority, was given to the hero.
1 Chronicles 27:4
ch1 27:4second month was Dodai--or, "Dodo." Here the text seems to require the supplement of "Eleazar the son of Dodo" (Sa2 23:9).
1 Chronicles 27:7
ch1 27:7Asahel--This officer having been slain at the very beginning of David's reign [Sa2 2:23], his name was probably given to this division in honor of his memory, and his son was invested with the command.
1 Chronicles 27:16
ch1 27:16PRINCES OF THE TWELVE TRIBES. (Ch1 27:16-24)
over the tribes of Israel: the ruler--This is a list of the hereditary chiefs or rulers of tribes at the time of David's numbering the people. Gad and Asher are not included; for what reason is unknown. The tribe of Levi had a prince (Ch1 27:17), as well as the other tribes; and although it was ecclesiastically subject to the high priest, yet in all civil matters it had a chief or head, possessed of the same authority and power as in the other tribes, only his jurisdiction did not extend to the priests.
1 Chronicles 27:18
ch1 27:18Elihu--probably the same as Eliab (Sa1 16:6).
1 Chronicles 27:23
ch1 27:23But David took not the number of them from twenty years old and under--The census which David ordered did not extend to all the Israelites; for to contemplate such an enumeration would have been to attempt an impossibility (Gen 28:14), and besides would have been a daring offense to God. The limitation to a certain age was what had probably quieted David's conscience as to the lawfulness of the measure, while its expediency was strongly pressed upon his mind by the army arrangements he had in view.
1 Chronicles 27:24
ch1 27:24neither was the number put in the account of the chronicles of King David--either because the undertaking was not completed, Levi and Benjamin not having been numbered (Ch1 21:6), or the full details in the hands of the enumerating officers were not reported to David, and, consequently, not registered in the public archives.
the chronicles--were the daily records or annals of the king's reign. No notice was taken of this census in the historical register, as from the public calamity with which it was associated it would have stood as a painful record of the divine judgment against the king and the nation.
1 Chronicles 27:25
ch1 27:25over the king's treasures--Those treasures consisted of gold, silver, precious stones, cedar-wood, &c.; those which he had in Jerusalem as distinguished from others without the city.
the storehouses in the fields--Grain covered over with layers of straw is frequently preserved in the fields under little earthen mounds, like our potato pits.
1 Chronicles 27:27
ch1 27:27the vineyards--These seem to have been in the vine growing districts of Judah, and were committed to two men of that quarter.
wine-cellars--The wine is deposited in jars sunk in the court of the house.
1 Chronicles 27:28
ch1 27:28olive trees and the sycamore trees . . . in the low plains--that is, the Shephela, the rich, low-lying ground between the Mediterranean and the mountains of Judah.
1 Chronicles 27:29
ch1 27:29herds that fed in Sharon--a fertile plain between CÃ&brvbr;sarea and Joppa.
1 Chronicles 27:30
ch1 27:30camels--These were probably in the countries east of the Jordan, and hence an Ishmaelite and Nazarite were appointed to take charge of them.
1 Chronicles 27:31
ch1 27:31rulers of the substance that was king David's--How and when the king acquired these demesnes and this variety of property--whether it was partly by conquests, or partly by confiscation, or by his own active cultivation of waste lands--is not said. It was probably in all these ways. The management of the king's private possessions was divided into twelve parts, like his public affairs and the revenue derived from all these sources mentioned must have been very large.