God was not obliged to restore it. Neither is there anything repugnant to faith and right reason that God could have restored the human race to His friendship by appointing some saint or angel to act as a representative of the whole race. We cannot restrict the wisdom and mercy and omnipotence of God. In order to have a full and adequate satisfaction, only Jesus Christ could perform the work of Redemption. Now, only such a person, a God-man, could offer adequate reparation for sin.
Sin involves a sort of infinite guilt because of the infinite dignity of the One offended.
Infinite guilt calls for infinite satisfaction. No saint or angel could offer such satisfaction to God. In fact, not even the human nature of Christ, as such, considered apart from the hypostatic union, could make such satisfaction. On the other hand, a divine person who was not at the same time man, could not perform the work of Redemption either. He could not represent the guilty human race.