‘ Then the Angel of Yahweh put out the end of the staff that was in his hand, and touched the flesh and the unleavened cakes, and there went up fire out of the rock, and consumed the flesh, and the unleavened cakes. And the Angel of Yahweh departed out of his sight.'
Yahweh gave Gideon the sign he had asked for. Note that He touched with His staff not the rock, but the sacrificial elements, the flesh and unleavened cakes, covered with the soup, a sign of His acceptance. And fire then arose and consumed them. Yahweh revealed Himself in fire and wholly accepted the offering. It was very similar to the burning bush except that there nothing was consumed.
We should note here that Gideon was not consciously acting as a priest. The angel of Yahweh was the priest accepting and offering up the offering. And although offerings under ‘green trees' were forbidden in Deuteronomy 12:2, that was in the case of sacred trees where altars had been built under them. There is no indication that this was a sacred tree.
“And the Angel of Yahweh departed out of his sight.” The sudden remarkable disappearance was final confirmation that he had been dealing with Yahweh Himself.