"All the articulated visions of prophecy are nothing more than ways of representing an abstract formless spiritual reality in the vocabulary of human language; although, to be sure, there may also be a revelation of an angel in quite ordinary form, clothed in some familiar vessel and manifested as a 'normal' phenomenon in nature.
The difficulty is that the one who sees angel in this way does not always know that it is an apparition, that the pillar of fire or the image of a man does not belong entirely to the realm of natural cause and effect.
And at the same time, the angel--that is to say, the force sent from a higher world--makes its appearance and to a certain extent acts in the material world, being either entirely subject to the laws of our world or operating in a sort of vacuum between the world in which physical nature is no more that a kind of garment for some higher substance.
In the Bible, Manoah, the father of Samson, sees the angel in the image of a prophet yet he senses in some inexplicable way that it is not a man he sees, that he is witnessing a phenomenon of a different order.
Only when the angel changes form completely and becomes a pillar of fire does Manoah recognize that this being, this marvel which he has seen and with whom he has conversed, was not a man, not a prophet, but a being from another dimension of reality--that is to say, an angel."
--Rabbi Adin Steinsaltz
From "Worlds" in The Thirteen Petalled Rose by Rabbi Adin Steinsaltz