City of God 10.6 is a rich and important, though obscure, explanation of what might be called the sociology of sacrifice. At the beginning of the chapter, Augustine defines sacrifice as any act we perform in order to be united to God in holy society. Acts of mercy are sacrifices, if they are done not only for the person whom we help but for God. (It is significant that Augustine does not define mercy as sacrifice because it involves loss; but, on the contrary, mercy is sacrificial because it is an act done toward God, who is our final happiness.)

But then Augustine moves from this general idea of sacrificial action to a consideration of Jesus’ Passion.

He states three premises: a) sacrifices are works of mercy directed to God, b) works of mercy are intended to liberate us from misery and make us blessed, and c) we cannot be liberated and blessed except by being near God (here quoting Psalm 73:28). From these premises, he concludes that the “whole redeemed city, that is the congregation and society of saints, is offered to God as a universal sacrifice through the great priest.” This priest offered Himself in the form of a servant with the intent of making us the body of such a head (tota ipsa redempta civitas, hoc est congregatio societasque sanctorum, universale sacrificium offeratur Deo per sacerdotem magnum, qui etiam se ipsum obtulit in passione pro nobis, ut tanti capitis corpus essemus, secundum formam servi).

It is not entirely clear how his premises lead to the conclusion that the city of God is itself a great, universal sacrifice. Perhaps Augustine means that the Passion is a great work of mercy by which Jesus drew near to His Father. It is also odd that Augustine speaks of the universal sacrifice of the city of God is offered in the Passion “for us.” It would seem that if the society of saints is the object being sacrificed, then that sacrifice cannot also be pro nobis .

Whatever the obscurities of the logic, the underlying principle is surely Augustine’s doctrine of the totus Christus . Christ offers Himself on the cross as mediator and head, and in that role is unique. But for Augustine this sacrifice is not just for us, but in some sense also the sacrifice of the redeemed City, the sacrifice that founds the redeemed city. His idea is a bit clearer when we remember His notion of sacrifice, namely, that it is any act by which we adhere to God in holy society. Jesus offered true sacrifice in precisely this sense, offering Himself on the cross in order to reach toward fellowship with His Father. And because He is the head of the body, His reaching for the Father brings us near into holy society with God.

Augustine concludes the chapter on a clearer note. Quoting Romans 12:3, he points to the connection between the “living sacrifice” and “transformation” that Paul demands and union in the body of Christ. He concludes “this is the sacrifice of Christians: ‘We, being many, are one body in Christ.’” We are constituted as one body in society with God through the cross, and we live out that sacrifice by acts of mercy, contrition, holiness in our lives with one another, as each of these practices is a vehicle for deepening union with God. Because the body and head form one Christ, service to one another is quite directly “referred” to God in Christ, since those we serve are one with Christ.

And at the very end of the chapter, Augustine notes that the Eucharist is the celebration of this ecclesial sacrifice of one body. This - that is, the fact that we, being many are one - “is the sacrifice which the Church continually celebrates in the sacrament of the altar, by which she demonstrates that she herself is offered in the offering that she makes to God.”