...His single matching our double

Augustine:

"To cure these and make them well the Word through which all things were made become flesh and dwelt among us (Jn. 1:14). Our enlightenment is to participate in the Word, that is, in that life which is the light of men (Jn. 1:4). Yet we were absolutely incapable of such participation and quite unfit for it, so unclean were we through sin, so we had to be cleansed. Futhermore, the only thing to cleanse the wick and the proud is the blood of the just man and the humility of God; to contemplate God, which by nature we are not, we would have to be cleansed by him who became what by nature we are and what by sin we are not. By nature we are not God; by nature we are men; by sin we are not just. So God became a just man to intercede with God for sinful man. The sinner did not match the just, but man did match man. So he applied to us the similarity of his humanity to take away the dissimilarity of our iniquity, and becoming a partaker of our mortality he made us partakers of his divninity (2 Pt. 1:4). It was surely right that the death of the sinner issueing from the stern necessity of condemnation should be undone by the death of the just man issuing from the voluntary freedom of mercy, his single matching our double."

- Augustine, On the Trinity, Book IV 1.4