Gideon said to him, Oh, my lord, if Yahweh is with us, why then has all this happened to us? and where are all his wondrous works which our fathers told us of, saying, Did not Yahweh bring us up from Egypt? but now Yahweh has cast us off, and delivered us into the hand of Midian.
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.