Solus Christus (Christ Alone) versus Totus Christus (the Whole Christ). If one wants to capture the difference between the evangelical faith and Roman Catholicism, here it is. On the one hand, the evangelical stress on the uniqueness of Jesus’s person (the God-man) and His atoning work; on the other, the Roman Catholic insistence on the organic relationship between Christ and the Church.
Essential to Roman Catholicism is what Gregg Allison has helpfully termed the “Christ-Church interconnection.” The Church is considered a prolongation of the Incarnation, mirroring Christ as a Divine-human reality, acting as an altera persona Christi, a second “Christ.” It is therefore impossible for Roman Catholicism to cry with the Reformers “solus Christus”, for this would be seen as breaching the organic bond between Christ and the Church. The threefold ministry of Christ as King, Priest, and Prophet is thus transposed to the Roman Church—in its hierarchical rule, its magisterial interpretation of the Word, and its administration of the sacraments. There is never solus Christus (Christ alone), only Christus in ecclesia (Christ in the Church) and ecclesia in Christo (the Church in Christ).
A Misleading View of Totus Christus
The origin of the “Christ-Church interconnection” goes back to a faulty interpretation by the Church father Augustine (354-430 AD) as he understood the relationship between Christ and the Church. One of the most controversial points of Augustine’s theology is his conception of the totus Christus, the “total Christ”: the idea that the unity of Christ with the Church is so deep as to form a single mystery. The Head of the body is so united with the body of the Head as to become a single Christ.
On this doctrine, Roman Catholicism built its own theology of the prolongation of the incarnation in the Church. It is as if there was such an intrinsic and profound union between Christ and the Church as to make it possible, indeed necessary, to see the Church as the sacramental extension of the incarnation of the Son of God. In fact, there are texts in which Augustine throws himself into one-sided statements in which, speaking of the Church united to Christ, he affirms “we are Christ” or “we have become Christ”. The whole Christ “is head and body”. At best, these would be ambiguous expressions if they had not been accompanied and supplemented by an orthodox Christology like that of Augustine. Besides the blurred statements about the totus Christus, speaking of Christ, Augustine writes that “even without us, He is complete”. Christ does not need the ecclesial body to be Christ. Elsewhere Augustine writes: “He is the Creator, we are the creatures; he is the craftsman, we are the work made by him, he the molder, we the molded ones”. His doctrine of the total Christ, however ambiguous and confused it is, does not break the distinction between Creator and creature and does not elevate the Church (the body) to a status of divinity.
Having said that, his interpretation of Colossians 1:24, Acts 9:4, and Ephesians 5 on the relationship between Christ and the Church in a spousal perspective led him to affirm the organic nature of that relationship and to go so far as affirming the “totality” of their being combined. The comments on the same texts also indicate the problematic direction of Augustine’s theology on the “deification” of the Christian, that is, his incorporation into the person of Christ becoming part of the mystical body. Indeed, one can understand how Roman Catholicism was dazzled by the metaphor of the total Christ, going far beyond Augustine and developing it in the theology of the Eucharist (the “real presence” of Christ) and the priesthood (the priest acting in altera Christi persona, in the person of Christ), and in the development of dogma (the Roman Church being endowed with the authority of Christ in promulgating dogmas). The Augustinian interpretation on this point is therefore subject to different uses, depending on what one wants to see in his texts as the primary element: the blurred totus Christus or the preserved distinction between Creator and creature.
Rome’s Appropriation of the Totus Christus
Rome interprets the Augustinian reference to totus Christus as a union, which confuses the distinction between the Head and the body. The Catechism of the Catholic Church teaches that “Christ and his Church thus together make up the ‘whole Christ’ (Christus totus). The Church is one with Christ” (§ 795). According to Subilia, in this mistake lies the “problem of Catholicism”. In his unsurpassed study, Subilia deals with the reason why the Church of Rome has such a high and excessive view of herself and is inclined to claim divine prerogatives. According to the Roman Catholic appropriation of Augustine’s formula, the relationship between Christ and the Church is so organic and profound that the Church becomes part of the whole Christ. Subilia notes that Augustine, who had been a Manichean, and therefore a dualist, suffered the opposite temptation of “monism” (i.e. the reduction to one) in his thought. While emphasizing the distinction between the Head and the members, and therefore between Christ and the Church, in Augustine “the sovereignty of the Head on the body is disastrously lost sight of” (p. 146). Defending Augustine and the Roman Catholic interpretation of the Church father, Catholic theologian Gherardini summarizes the ecclesiology of the totus Christus as “Christ continued and identified in the Church”.
Starting from Augustine, Roman Catholic ecclesiology became radicalized in emphasizing the theme of the unity between Christ and the Church in terms of a hierarchical-sacramental church representing Christ on earth. For Subilia, this is a “radical devastation that has changed the vital centers of the Christian organism and transformed it into a different organism” (p. 150). If this reading is plausible, the “problem of Catholicism” is not merely in one doctrine or in some superficial differences on secondary issues. Its problem lies at the very heart of its system and is pervasively present in all its expressions: from the Trinity to Mariology, from the sacraments to soteriology, from ecclesiology to the manifold devotions. All is infected by the totus Christus.
Back to Solus Christus
The Protestant Reformation was an attempt to face the damages of this inflated and distorted Christianity by putting the totus Christus back within its biblical boundaries. By arguing that the faith and life of the Church needed to be grounded on Scripture alone (Sola Scriptura), the Reformers wanted to reaffirm that the authority of God is exercised by Scripture over the Church. The totus Christus allowed the Roman Church to claim to have authority to promulgate new dogmas without Scriptural support and to endorse teachings and practices that went against the Bible. Sola Scriptura was a reminder that the Church is subject to the authority of God in the Bible.
By confessing that salvation comes to us by faith alone (Sola Fide), the Reformers wanted to recognize that we are saved by an external gift achieved by Christ alone and given to us by grace. There is nothing in us that deserves it. The Roman Catholic totus Christus had built a sophisticated system whereby the Church contributes to salvation through its sacramental system and the faithful merits it through his good works. Sola Fide was a reminder that the gospel is indeed Good News because Jesus Christ alone has accomplished what is needed for our salvation. Salvation needs to be received by faith alone.
Ultimately, the Protestant Reformation wanted to re-focus the whole of the Christian faith and life on Christ Alone (Solus Christus): the Son of God incarnate, the Lord Jesus Christ, Saviour of the world. The misinterpretation of Augustine’s totus Christus led the Roman Catholic Church to deviate from the biblical faith by endorsing an inflated view of Mary and the saints as mediators, an exaggerated view of the Church as the hierarchical and sacramental institution prolonging the incarnation, and an optimistic view of man’s ability to contribute to salvation. Solus Christus is the best corrective to a blurred understanding of totus Christus and the best safeguard against the intrusion of alien elements into the Christian faith. Whether or not this was Augustine’s intention (and this is disputed), this is nonetheless the biblical medicine to recover the evangelical, Trinitarian, orthodox faith that was once for all entrusted to God’s holy people (Jude 3).
 S. Wellum, Christ Alone, The Uniqueness of Jesus as Saviour. What the Reformers Taught and Why It Still Matters (Grand Rapids, MI: Zondervan, 2017).
 G.R. Allison, Roman Catholic Theology and Practice. An Evangelical Assessment (Wheaton, IL: Crossway, 2014) pp. 42-67.
 Here I rely on this collection of Augustine’s texts on the topic: Sant’Agostino, Il Cristo totale, ed. G. Carrabetta (Roma: Città Nuova, 2012).
 On this point see D.V. Meconi, The One Christ. St. Augustine’s Theology of Deification (Lanham, MD: The Catholic University of America Press, 2013).
 V. Subilia, The Problem of Catholicism (Philadelphia, PA: Westminster Press, 1964).
 B. Gherardini, La Cattolica. Lineamenti d’ecclesiologia agostiniana (Torino: Lindau, 2011) p. 29.