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.
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Augustine of Hippo
For if an angel is able to use air, mist, cloud, fire, and any other natural substance or physical species; and a person [is able] to use, face, tongue, hand, pen, letters, or any other means for the purpose of communicating the secret things of his own mind: in a word, if, though he is human, he sends human messengers, and he says to one, “Go,” and he goes; and to another, “Come,” and he comes; and to his servant, “Do this,” and he does it”; with how much greater and more effectual power does God—to whom, as Lord, all things are subject—use both angel and man in order to declare whatever pleases him? - "Explanations of the Psalms 78.5"