I have been doing a little bit of study on the doctrine of totus Christus. From my viewpoint, many Catholic distinctives stem from this doctrine. The Catechism of the Catholic Church speaks of this in paragraph 795:
Christ and his Church thus together make up the “whole Christ” ( Christus totus ). The Church is one with Christ. The saints are acutely aware of this unity:
Let us rejoice then and give thanks that we have become not only Christians, but Christ himself. Do you understand and grasp, brethren, God’s grace toward us? Marvel and rejoice: we have become Christ. For if he is the head, we are the members; he and we together are the whole man . . . . the fullness of Christ then is the head and the members. But what does “head and members” mean? Christ and the Church. [St. Augustine, In Jo. ev , 21, 8: PL 35, 1568]
Our redeemer has shown himself to be one person with the holy Church whom he has taken to himself. [Pope St. Gregory the Great, Moralia in Job , praef., 14: PL 75, 525A]
Head and members form as it were one and the same mystical person. [St. Thomas Aquinas, ST III.48.2]
A reply of St. Joan of Arc to her judges sums up the faith of the holy doctors and the good sense of the believer: “About Jesus Christ and the Church, I simply know they’re just one thing, and we shouldn’t complicate the matter.”
Here is the summary paragraph that I have come up with.
Typically Protestants take the “body of Christ” to be a metaphor similar to other images the NT used to discuss the nature and function of the church. But Catholic and Orthodox theologians see 1 Corinthians 12:27 where Paul says “you are Christ’s body” as more than a mere metaphor, but a statement of reality speaking to the indissoluble relationship between Christ and his church. This has become know as the doctrine of totus Christus, which asserts the identity between Christ and his church is so complete that Christ and his church are now one and the same person. Through the Spirit, Christ is organically united to his body, the Church, so that he is with her totus Christus, caput et membra (the whole Christ, head and members). Christ and his church are not only related conceptually, but ontically and metaphysically. The two have become one singular reality.
Student: Does ‘Body of Christ’ have any sociological meaning for you?
Barth: Yes, if seen Christologically. The Church is indirectly identical with Jesus Christ. He is not without his Body. We believe in the totus Christus, and that includes his body on earth. But it is a living body, so we came back to the notion of event.
Student: Is the body an event?
Barth: Yes, bodily existence is an event.
Student: Is it not dangerous to say totus Christus?
Barth: No, we are only Christ’s Body, not the head. This means that we can never have a ‘head’ of the Church on earth; this is the Roman Catholic heresy.
Student: But should we say that his body is not yet perfect?
Barth: I would rather say, ‘His body is not yet revealed.’ What we see is imperfection, but what we need is apokalypsis.”
~ Noted by Mangina, Karl Barth: Theologian of Christian Witness, 165.