Judges 6:11
And there came an angel of the LORD, and sat under an oak which was in Ophrah, that pertained unto Joash the Abi-ezrite: and his son Gideon threshed wheat by the winepress, to hide it from the Midianites. And there came an angel of the LORD, and sat under an oak which was in Ophrah, that pertained unto Joash the Abi-ezrite: and his son Gideon threshed wheat by the winepress, to hide it from the Midianites.
This moment belongs to Israel's repeated cycle of apostasy followed by oppression and then deliverance, when for seven years the Midianites ravaged the land, stripped away its harvests, and drove the Israelites from their homes. After seven years of such distress the people confessed their sins, and in response God raised up a helper to deliver them. Gideon himself was secretly threshing a small amount of wheat by the winepress, hiding his work from the Midianites for fear they would seize it.
He had chosen that place rather than the usual threshing floor because the grape harvest was still far off and the vineyards drew little notice. As he labored there he grieved over Israel's oppression and turned his thoughts to how its yoke might be broken. It was while he was engaged in this humble work of threshing that the Angel of the Lord came to him, calling and choosing him to serve as God's instrument to deliver Israel from its enemies.