Matthew Poole and continuators on Judges 13:20

20 For it came to pass when the flame went up toward heaven from off the altar , that the angel of the LORD ascended in the flame of the altar: and Manoah and his wife looked on it, and fell on their faces to the ground.

Either arising from the fire which Manoah brought for the offering: or produced by the Angel out of the Rock in a miraculous manner.

i. e. From that part of the Rock which served instead of an Altar, upon which the Sacrifice was laid.

To manifest his nature and essence to be Spiritual, because not capable of hurt by the fire; and Caelestial.

Partly in Reverence to that glorious Presence manifested in so wonderful a manner: and partly, out of a religious Horror and fear of death upon this occasion; as is expressed v. 22. for the prevention whereof they fell down in way of supplication to God.