Charles Ellicott Commentary Joshua 8:3

"So Joshua arose, and all the people of war, to go up to Ai: and Joshua chose out thirty thousand men, the mighty men of valor, and sent them forth by night." — Joshua 8:3 (ASV)

And Joshua chose out thirty thousand mighty men. — Some difficulty arises from the fact that thirty thousand men are mentioned as having been sent away with general instructions to form an ambush in the first instance, while five thousand were ultimately posted between Bethel and Ai. Were there two distinct bodies in ambush, or only one? It does not seem possible to answer this question with absolute certainty; but we ought to notice, in the first place, what Joshua's aim was. He meant to isolate the town of Ai, taking it in front and flank; but there was another town immediately in the rear, less than two miles away. It was necessary, therefore, to employ a sufficient body of men to cut off communications between Bethel and Ai from the outset.