Who but the God-man?

In his Institutes of the Christian Religion, Calvin addresses why it is that humans needed God to become man in order to mediate our reconciliation to God successfully.

...it was also imperative that he who was to become our Redeemer be true God and true man. It was his task to swallow up death. Who but the Life could do this? It was his task to conquer sin. Who but very Righteousness could do this? It was his task to rout the powers of world and air. Who but a power higher than world and air could do this? Now where does life or righteousness, or lordship and authority of heaven lie but with God alone? Therefore our most merciful God, when he willed that we be redeemed, made himself our Redeemer in the person of his only-begotten Son [cf. Rom. 5:8].