“God might have acted, in this respect, by himself, without any aid or instrument, or might even have done it by angels; but there are several reasons why he rather chooses to employ men. First, in this way he declares his condescension towards us, employing men to perform the function of his ambassadors in the world, to be the interpreters of his secret will; in short, to represent his own person. Thus he shows by experience that it is not to no purpose he calls us his temples, since by man’s mouth he gives responses to men as from a sanctuary. Secondly, it forms a most excellent and useful training to humility, when he accustoms us to obey his word though preached by men like ourselves, or, it may be, our inferiors in worth. Did he himself speak from heaven, it were no wonder if his sacred oracles were received by all ears and minds reverently and without delay. For who would not dread his present power? who would not fall prostrate at the first view of his great majesty? who would not be overpowered by that immeasurable splendour? But when a feeble man, sprung from the dust, speaks in the name of God, we give the best proof of our piety and obedience, by listening with docility to his servant, though not in any respect our superior. Accordingly, he hides the treasure of his heavenly wisdom in frail earthen vessels (2 Cor. 4:7), that he may have a more certain proof of the estimation in which it is held by us.”

John Calvin, Institutes of the Christian Religion, Chapter 3