Then Gideon took ten men of his servants, and did as Yahweh had spoken to him: and it happened, because he feared his father's household and the men of the city, so that he could not do it by day, that he did it by night.
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.