Then the angel of Yahweh put forth the end of the staff that was in his hand, and touched the flesh and the unleavened cakes; and there went up fire out of the rock, and consumed the flesh and the unleavened cakes; and the angel of Yahweh departed out of his sight.
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.