The angel of Yahweh came, and sat under the oak which was in Ophrah, that pertained to Joash the Abiezrite: and his son Gideon was beating out wheat in the winepress, to hide it from the Midianites.
To confirm that the Angel really was a divine messenger, Gideon requested some supernatural confirmation that this calling was from God (Judges 6:17). He then prepared to offer his guest a token of his hospitality (Judges 6:18).