NOTES for Jdg 13:20-21
The Bible generally tells us little about angels and their nature; they usually appear on the biblical pages only as messengers of God's will, disappearing immediately after fulfilling what was entrusted to them. Judging by the few descriptions, one of which is the description of the angel's appearance to Manoah, angels are created beings, but they possess an entirely special nature, not comparable with the nature of the physical world.
An angel's contact with this nature causes immediate annihilation of physical substance - it simply burns up, as the food offered to the angel by Manoah burned in the fire, and the angel himself disappears in the tongue of flame. Here physical fire is mixed with something else, something inaccessible to any research or study by traditional means, but whose nature, among earthly realities, most resembles fire, at least outwardly.
Meanwhile the main task of God's messenger in this case was to indicate God's plan concerning the future child, who would possess special abilities, so that for his mother, who was carrying him, the most proper thing was to live the life of a person who had taken Nazirite vows; for her son too, as God's messenger says of him, would be a Nazirite all his life. This was unusual: as a rule, Nazirite vows were taken only for a time one wished to spend in more intense communion with God. Here, however, the matter was a life wholly dedicated to God, when a person gives himself completely into God's hands. It was not yet clear what the life of this person not yet born into the world would be like, but it was already obvious that it would be unusual.