John Calvin Commentary Joshua 8:1

"And Jehovah said unto Joshua, Fear not, neither be thou dismayed: take all the people of war with thee, and arise, go up to Ai; see, I have given into thy hand the king of Ai, and his people, and his city, and his land;" — Joshua 8:1 (ASV)

And the Lord said unto Joshua, and so forth. It was of great consequence to Joshua, as well as the people, to inspire new courage, so that they might prepare with confidence to assault the city of Ai, from which they had recently been repulsed with loss and greater disgrace. God, therefore, to inspire them with fearlessness on this expedition, promised that He would give them the city. With the same aim, He instructed them to fight by stratagem more than open war, to entice the enemy out, and to select a secret place for an ambush that might take them by surprise.

A few thousand might have been overthrown without any difficulty by an immense host attacking the city suddenly and unexpectedly. But as we previously saw that the hearts of all had melted away, God accommodated their weakness by laying no greater burden on them than they were able to bear, until they had recovered from their excessive panic and could execute His commands with eagerness.

It is true, indeed, that He now used their own effort, partly so that they might not always keep looking for miracles and thus give themselves up to laziness, and partly so that in different and varying ways of acting they might nevertheless recognize that His power is the same. But care must be taken not to overlook the special reason: namely, that since they had not yet recovered from their terror, they could hardly have been persuaded to engage in an open conflict if they had not seen stratagem employed as additional support.

Primary importance, however, is given to the promise: Fear not, for I have delivered it into thy hands. For although it was spoken to Joshua, it applied equally to all the people, since it was essential that every single one of them should be freed from anxiety and filled with new confidence.

The order to burn the city like Jericho appears to be a concession to public sentiment, as the vengeance taken in this way served to erase the memory of their disgrace. At the same time, so that they might engage in the expedition more willingly, the spoils were left to them as the reward of victory.