What is the wisdom behind Allah's provision of a thousand angels to the Muslims in the Battle of Badr, despite the ability of a single angel, such as Gabriel, to defeat an entire army?

The descent of the angels was glad tidings for the believers, so that their hearts would be at peace. Allah made the fighting of the angels a support and aid for the people of faith, while keeping the actual fighting for the believers, in observance of the means and Allah's way with His creation. The true victory is from Allah alone.