Saint Anselm,
Cur Deus Homo — Book Second, Chapter XXI
“ For, as man could not be reconciled but by the death of the God-man, by whose holiness the loss occasioned by man's sin should be made up; so fallen angels cannot be saved but by the death of a God-angel who by his holiness may repair the evil occasioned by the sins of his companions. And as man must not be restored by a man of a different race, though of the same nature, so no angel ought to be saved by any other angel, though all were of the same nature, for they are not like men, all of the same race. For all angels were not sprung from one, as all men were. ”
