Then all the Midianites and the Amalekites and the children of the east assembled themselves together; and they passed over, and encamped in the valley of Jezreel.
So here was Gideon hiding from the Midianites as he was threshing the wheat because if the Midianites had caught him they'd take the wheat. And so he was out by the winepress threshing wheat and here was an angel sitting under an oak tree.