From St. Leo the Great
"To pay the debt of our sinful state, a nature that is incapable of suffering was joined to one that could suffer. Thus, in keeping with the healing that we needed, one and the same mediator between God & Men, the man Jesus Christ, was able to die in one nature and unable to die in the other.
He who is true God was therefore born in the complete and perfect nature of a true man, whole in his own nature, whole in ours. By our nature, we mean what the Creator had fashioned in us from the beginning and took to himself in order to restore it."