Matthew Henry on 2 Samuel 18:1-8
Which way David raised an army here, and what reinforcements were sent him, we are not told; many, it is likely, from all the coasts of Israel, at least from the neighbouring tribes, came in to his assistance, so that, by degrees, he was able to make head against Absalom, as Ahithophel foresaw. Now here we have,
I. His army numbered and marshalled, Sa2 18:1, Sa2 18:2. He had, no doubt, committed his cause to God by prayer, for that was his relief in all his afflictions; and then he took an account of his forces. Josephus says they were, in all, but about 4000. These he divided into regiments and companies, to each of which he appointed proper officers, and then disposed them, as is usual, in…
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And set captains of thousands - By this time David's small company was greatly recruited; but what its number was we cannot tell. Josephus says it amounted to four thousand men. Others have supposed that they amounted to ten thousand; for thus they understand a clause in Sa2 18:3, which they think should be read, We are now ten thousand strong.
John Gill on 2 Samuel 18:1
And David numbered the people that were with him,.... Which Josephus says (d) were four thousand; but one would think there should be more by what follows:
and set captains of thousands and captains of hundreds over them; he divided his army into companies, which consisted some of a thousand and others of a hundred; over each of which he set captains, to lead them on, direct, and command them in battle.
(d) Antiqu. l. 7. c. 10. sect. 1.