Clement of Alexandria

"And if any man sin," he says, "we have an advocate with the Father, Jesus Christ." For so the Lord is an advocate with the Father for us. So also is there, an advocate, whom, after His assumption, He vouchsafed to send. For these primitive and first-created virtues are unchangeable as to substance, and along with subordinate angels and archangels, whose names they share, effect divine operations. Thus also Moses names the virtue of the angel Michael, by an angel near to himself and of lowest grade. The like also we find in the holy prophets; but to Moses an angel appeared near and at hand. Moses heard him and spoke to him manifestly, face to face. On the other prophets, through the agency of angels, an impression was made, as of beings hearing and seeing.

On this account also, they alone heard, and they alone saw; as also is seen in the case of Samuel. Elisaeus also alone heard the voice by which he was called. If the voice had been open and common, it would have been heard by all. In this instance it was heard by him alone in whom the impression made by the angel worked.