1 Chronicles 27:1 - Clarke's commentary and critical notes on the Bible

Now the children of Israel after their number, to wit, the chief fathers and captains of thousands and hundreds, and their officers that served the king in any matter of the courses, which came in and went out month by month throughout all the months of the year, of every course were twenty and four thousand. The chief fathers and captains of thousands - The patriarchs, chief generals, or generals of brigade. This enumeration is widely different from the preceding. In that, we have the orders and courses of the priests and the Levites in their ecclesiastical ministrations; in this, we have the account of the order of the civil service, that which related simply to the political state of the king and the kingdom. Twenty-four persons, chosen out of David's worthies, each of whom had a second, were placed over twenty-four thousand men, who all served a month in turn at a time; and this was the whole of their service during the year, after which they attended to their own affairs. Thus the king had always on foot a regular force of twenty-four thousand, who served without expense to him or the state, and were not oppressed by the service, which took up only a twelfth part of their time, and by this plan he could at any time, when the exigency of the state required it, bring into the field twelve times twenty-four thousand, or two hundred and eighty-eight thousand fighting men, independently of the twelve thousand officers, which made in the whole an effective force of three hundred thousand soldiers; and all these men were prepared, disciplined, and ready at a call, without the smallest expense to the state or the king. These were, properly speaking, the militia of the Israelitish kingdom. See Calmet.