John Gill Commentary Joshua 8:9

"And Joshua sent them forth; and they went to the ambushment, and abode between Beth-el and Ai, on the west side of Ai: but Joshua lodged that night among the people." — Joshua 8:9 (ASV)

Joshua therefore sent them forth
The thirty thousand chosen men:

and they went to lie in ambush ;
as they were ordered, (Joshua 8:2) :

and abode between Bethel and Ai, on the west side of Ai ;
for as Ai was on the east of Bethel, (Joshua 7:2) . Bethel must be on the west of Ai, as Jarchi notes:

but Joshua lodged that night among the people ;
the main body of the army, to direct them in the affair of war, how they should behave the next day, when they came to fight;

And to inspire them with courage and confidence, that they might not be afraid, because of their having been smitten before by this people, so Ben Gersom; or rather that he and they might be ready in the morning to march towards Ai, as Jarchi and Kimchi.