How the redemption of man could not be effected by any other being but God.
Boso. If this deliverance were said to be effected somehow by any other being than God (whether it were an angelic or a human being), the mind of man would receive it far more patiently. For God could have made some man without sin, not of a sinful substance, and not a descendant of any man, but just as he made Adam, and by this man it should seem that the work we speak of could have been done.
Anselm. Do you not perceive that, if any other being should rescue man from eternal death, man would rightly be adjudged as the servant of that being? Now if this be so, he would in no wise be restored to that 185dignity which would have been his had he never sinned. For he, who was to be through eternity only the servant of God and an equal with the holy angels, would now be the servant of a being who was not God, and whom the angels did not serve.
Source: Cur Deus Homo (CCEL)