7 And we know that the eunuch who was reading Isaiah the prophet, and did not understand what he read, was not sent by the apostle to an angel, nor was it an angel who explained to him what he did not understand, nor was he inwardly illuminated by the grace of God without the interposition of man; on the contrary, at the suggestion of God, Philip, who did understand the prophet, came to him, and sat with him, and in human words, and with a human tongue, opened to him the Scriptures. Did not God talk with Moses, and yet he, with great wisdom and entire absence of jealous pride, accepted the plan of his father-in-law, a man of an alien race, for ruling and administering the affairs of the great nation entrusted to him? For Moses knew that a wise plan, in whatever mind it might originate, was to be ascribed not to the man who devised it, but to Him who is the Truth, the unchangeable God.
Source: Christian Doctrine (New Advent)