It deeply concerned us, that he who was to be our Mediator should be very God and very man. If the necessity be inquired into, it was not what is commonly termed simple or absolute, but flowed from the divine decree on which the salvation of man depended. What was best for us, our most merciful Father determined. Our iniquities, like a cloud intervening between Him and us, having utterly alienated us from the kingdom of heaven, none but a person reaching to him could be the medium of restoring peace. But who could thus reach to him? Could any of the sons of Adam? All of them, with their parents, shuddered at the sight of God. Could any of the angels? They had need of a head, by connection with which they might adhere to their God entirely and inseparably. What then? The case was certainly desperate, if the Godhead itself did not descend to us, it being impossible for us to ascend. Thus the Son of God behoved to become our Emmanuel, the God with us; and in such a way, that by mutual union his divinity and our nature might be combined.
John Calvin, Institutes of the Christian Religion, 2.12.1.