Joshua 8:29

And the king of Ai he hanged on a tree until eventide, Numbers 25:4; and as soon as the sun was down, Joshua commanded that they should take his carcass down from the tree, Deuteronomy 21:23, and cast it at the entering of the gate of the city, and raise thereon a great heap of stones, that remaineth unto this day. The entire story teaches that we should indeed use all our physical and mental powers in the work given us by the Lord, but that everything depends upon His almighty power and blessing. It is He who must give us the victory in every battle.