that Yahweh sent a prophet to the children of Israel: and he said to them, Thus says Yahweh, the God of Israel, I brought you up from Egypt, and brought you forth out of the house of bondage;
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.