John Gill Commentary Joshua 8

And the Lord said unto Joshua
Immediately after the execution of Achan, the fierceness of his anger being turned away:

fear not, neither be you dismayed ;
on account of the defeat of his troops he had sent to take Ai:

take all the people of war with you ;
all above twenty years of age, which, with the forty thousand of the tribes on the other side Jordan he brought over with him, must make an arm, five hundred thousand men; these Joshua was to take with so much to animate and encourage him, or to terrify the enemy, nor because such a number was necessary for the reduction of Ai, which was but a small city; but that all might have a part in the spoil and plunder of it, which they were denied at Jericho, and chiefly to draw all the men out of the city, seeing such a numerous host approaching:

and arise, go up to Ai ;
which lay high, and Joshua being now in the plains of Jericho, (See Gill on Joshua 7:2);

see, I have given into your hand the king of Ai, and his people, and
his city, and his land ;
this city, though a small one, had a king over it, as most cities in the land of Canaan had; the number of his people in it were twelve thousand, and his land were the fields about it; all which were given to Joshua by the Lord, and were as sure as if he had them already in his hand.

And you shall do to Ai and her king as you did to Jericho
and her king
Burn the one and slay the other:

only the spoil thereof, and the cattle thereof, shall you take for a
prey unto yourselves ;
which they were not allowed to do at Jericho:

lay thee an ambush for the city behind it ;
at the west side of it: some have called in question the lawfulness of the ambush, but, as this was appointed by the Lord, there is no room for it.

So Joshua arose, and all the people of war, to go up against
Ai
As the Lord had commanded him:

and Joshua chose out thirty thousand mighty men of valour ;
out of all the men of war; these were a select company, picked men, not the whole army, as some have thought, for he was ordered to take all the people of war, as he did:

and sent them away by night ;
from the main army, that they might pass the city and get behind it undiscovered, for they were sent for an ambush; and of these some were to take the city, and be left in it to burn it, and some to smite the men of Ai, as Abarbinel notes.

And he commanded them, saying
At the time he sent them away;

behold, you shall lie in wait against the city, [even] behind the city ;
that is, on the west side of it, (Joshua 8:9) ;

go not very far from the city, but be you all ready ;
to enter into it, as soon as the forces are drawn out eastward to meet the army of Israel.

And I and all the people that [are] with me will approach unto
the city
That is, Joshua with the main body of the army would march up to the city the next morning, in order to draw out the inhabitants of it to fight them:

and it shall come to pass, when they come out against us, as at the
first ;
as they had done before, when the three thousand were sent against them, (Joshua 7:4Joshua 7:5) ;

that we will flee before them ;
as the three thousand did, which would animate them to pursue them with the greater eagerness, and to a distance from their city.