Roman Catholic theology is the doctrinal system and individual dogmas developed and defended by the Roman Catholic Church. The system is grounded on two axioms—the nature-grace interdependence and the Christ-Church interconnection—from which flow the various Catholic beliefs.


This essay focuses on Roman Catholic theology in relationship to Protestant theology. The foundations of the Catholic system are the nature-grace interdependence and the Christ-Church interconnection. The foundations of the Protestant system are the Reformation principles encapsulated in five solas: Scripture alone, Christ alone, grace alone, faith alone, God’s glory alone. Still, the two traditions embrace many commonalities. At the same time, because the two systems have different foundations, they clash with many theological divergences.


The Christian religion and the theology associated with it encompass three major branches: Roman Catholicism, Eastern Orthodoxy, and Protestantism. This article addresses the first of these traditions, with a focus on Roman Catholic theology in relationship to Protestant theology.

When people consider the Roman Catholic Church, they tend to think of the authority of the pope, the veneration of Mary, the celebration of the Mass, the Eucharist and the other sacraments, and the like. The theology undergirding these various doctrines and practices rests on two foundations: the nature-grace interdependence and the Christ-Church interconnection.

The Nature-Grace Interdependence

By way of definition, nature is whatever has been created: planets, angels, mountains, trees, birds, fish, animals, human beings, water, oil, bread, and wine. Grace is God’s favor in relation to the world he created. According to Roman Catholic theology, nature and grace are, by God’s design, interdependent. Nature is capable of receiving and transmitting grace, and grace must be concretely communicated by nature. For example, water (in the realm of nature) is capable of receiving and communicating grace when, consecrated by a Catholic bishop, it is used for Baptism. This sacrament (in the realm of grace) cleanses an infant from original sin, regenerates, and incorporates him/her into Christ and his Church. This nature-grace interdependence is the first foundation of Catholic theology.

The Christ-Church Interconnection

There are two manifestations of the principle of incarnation, a pattern with which God created the world so that grace and nature would be interdependent. The first manifestation is the incarnation of the Son of God as Jesus Christ, who mediated grace to nature. The second manifestation is the Roman Catholic Church, which, as the prolongation of the incarnation of Christ, continues to mediate grace to nature. The Church is the continuation of God the Son incarnate, being the whole Christ—deity, humanity, and body.

Accordingly, the Roman Catholic Church acts as another (or second) person of Christ, mediating between the two realms of nature and grace. Nature, being open to grace, receives the grace mediated to it by the Church. Grace, which must be tangible and concrete, is communicated through elements of nature that are consecrated by the Church. For example, a Catholic bishop consecrates oil (in the realm of nature) and employs it for the sacraments of Confirmation and Holy Orders. Mediating these sacraments in the place of Christ, the Church tangibly and concretely confers grace upon those being confirmed and those entering the priesthood. This Christ-Church interconnection is the second foundation of Catholic theology.

Roman Catholic theology is built upon these two foundations. Protestant theology, in particular, disagrees with these axioms, having its own Reformation principles encapsulated in its five solas: Scripture alone, Christ alone, grace alone, faith alone, God’s glory alone. Catholic theology and Protestant theology are constructed on very different foundations.


Still, as a tradition within the broad Christian religion, Roman Catholic theology has many commonalities with the other two traditions, Eastern Orthodoxy and Protestantism. These doctrinal agreements include the following:

  1. The Trinity: God eternally exists as Father, Son, and Holy Spirit.
  2. The nature of God: God is self-existent, unchangeable, eternal, everywhere present, all-powerful, all-knowing, loving, holy, just, glorious, and the like.
  3. The revelation of God: God reveals himself through both general revelation (e.g., creation and the human conscience) and special revelation (e.g., the Son’s incarnation and inspired communication).
  4. The person of Jesus Christ: The Son became incarnate as Jesus Christ, being conceived by the Holy Spirit and born of the Virgin Mary. He is the God-man, possessing a fully divine nature and a fully human nature.
  5. The saving work of Jesus Christ: God the Son incarnate lived a sinless life, at the end of which he was crucified for our sins, died, and was buried.
  6. The person and work of the Holy Spirit: The Holy Spirit is worshiped together with the Father and the Son and works inseparably with them in creation, providence, redemption, and consummation.
  7. The glory and depravity of human beings: God created human beings as the pinnacle of his creation. As divine image bearers, they are complex persons of both a material aspect (body) and immaterial aspect (soul or spirit). Adam and Eve fell into sin, and the entire human race was plunged into sin. Original sin is the state of corruption (and guilt, according to some) into which all human beings are born.
  8. Salvation is initiated by God: The divine initiative in accomplishing salvation focuses on Jesus Christ’s death by crucifixion as an atoning sacrifice for human sin. Having accomplished salvation, he rose from the dead on the third day and later ascended into heaven, from which he sent the Holy Spirit. The divine initiative in applying salvation focuses on God’s mighty acts of election, calling people to himself, gracious prompting toward repentance and faith, and more. No role for human initiative and merit at the outset of salvation is allowed.
  9. The community of faith: The church is characterized by four attributes: oneness (unity), holiness (purity), catholicity (universality), and apostolicity (associated with the apostles). It is the people of God, the body of Christ, and the temple of the Holy Spirit.
  10. The living hope: The personal hope of Christians is to escape eternal punishment and enjoy eternal life. The cosmic hope of Christians includes the second coming of Jesus Christ, the resurrection of the body, the appearance before Christ at the last judgment, and live everlasting in the new heaven and new earth.


Roman Catholic theology has significant differences with the other two traditions, particularly Protestant theology. Foundationally, these divergences flow from the nature-grace interdependence and the Christ-Church interconnection, the two axioms disputed by Protestantism. Specifically, these doctrinal disagreements include the following:

  1. Divine revelation and its interpretation: According to Roman Catholicism, authoritative revelation from God consists of two tightly connected streams, Scripture and Tradition. According to Protestantism, divine revelation is Scripture only (sola Scriptura, one of the foundational Protestant principles).
    • Scripture is the Word of God inspired by the Holy Spirit and written by human authors. Whereas the Roman Catholic Bible and the Protestant Bible are identical with regard to the New Testament, they differ on the composition of the Old Testament. The Protestant Old Testament has thirty-nine writings, and the Roman Catholic Old Testament has an additional seven books—Tobit, Judith, Wisdom of Solomon, Ecclesiasticus, Baruch, and 1 and 2 Maccabees—and additional sections in Esther and Daniel. These writings, called the Apocrypha, were not part of the Bible of Jesus and his apostles; for this reason they are not included in the Protestant Old Testament.
    • Tradition is teaching that Jesus communicated orally to his apostles, who, in turn, communicated it orally to their successors, the bishops. This Tradition is maintained by the Roman Catholic Church’s teaching office, or Magisterium, which occasionally proclaims doctrines based on it (e.g., the immaculate conception of Mary and her bodily assumption). Protestant theology dismisses this notion of Tradition because of its poor biblical and historical support, and because it contradicts the sole authority, sufficiency, and necessity of Scripture.
    • The interpretation of divine revelation, according to Roman Catholicism, is the responsibility of the Church’s hierarchy. The Magisterium, consisting of the pope and the bishops, provides the Church with the authoritative interpretation of written Scripture and Tradition. Accordingly, all Catholic interpretations must conform to the Magisterium’s official interpretation. Protestant biblical interpretation operates from the clarity of Scripture and the illumination of the Holy Spirit in concert with basic interpretive principles; for example, the theme of all Scripture is Christ, and different genres—narrative, poetry, letter, prophecy, proverb—have different rules for understanding them.
  2. Mariology: According to Roman Catholicism, Mariology consists of several core elements. In eternity past, God planned that the incarnation of the Son would be preceded by assent on the part of a woman predestined to become his mother. For this key woman to agree to her predestined role, she had to be well prepared. Accordingly, Roman Catholic theology invokes the immaculate conception of Mary: at her conception, she “was preserved immune from all stain of original sin” (Pius IX, Ineffabilis Deus, December 8, 1854). Conceived without sin, she was born without sin and lived her entire life without sin. Thus, at the angel’s announcement that she would become the mother of Son of God, Mary gave her assent to the will of God.
    • Mary’s sinlessness was manifested by her perpetual virginity; she remained a virgin her whole life. Moreover, Catholic theology maintains a special role for Mary in the Church. As her Son was being crucified, she suffered with him and consented to his sacrificial offering on the cross. As one of his last acts, Jesus entrusted Mary to be the mother of all Christians. Following Jesus’ ascension, Mary prayed to help inaugurate the Church. Therefore, she is the model of obedience, faith, suffering, and hope for the Church, of which she is the mother. In light of her sinlessness, Roman Catholic theology invokes the bodily assumption of Mary: “when the course of her earthly life was finished, [she] was taken up body and soul into heavenly glory” (Pius XII, Munificentissimus Deus, November 1, 1950).
    • This exalted Mariology is clearly seen in the titles by which the Church invokes Mary: Advocate, Helper, Benefactress, and Mediatrix. The Church is devoted to her in a special way—not the devotion of worship, which is reserved for God alone, but not merely veneration, which is given to all the saints. Rather, the devotion to Mary is hyperdulia (or super-veneration), which includes prayer for her intercession for the Catholic faithful and aid for her gracious intervention on their behalf.
    • Protestant theology gratefully acknowledges Mary as the mother of Jesus Christ, appreciates her outstanding example of faith and obedience, and calls her “blessed” (Luke 1:48) because of God’s mighty work in and through her. It rejects, however, the developed Roman Catholic Mariology.
  3. The Church and its sacraments: On the basis of the nature-grace interdependence and the Christ-Church interconnection, the Roman Catholic Church claims to be the sole Church of Christ. Thus, Protestant assemblies are not real churches but “ecclesial communities” whose salvation flows from the fullness of salvation in the Catholic Church.
    • Structurally, at the heart of the Church is the pope, who is the successor of Peter and the Vicar, or representative, of Christ, along with the bishops, who constitute the Church’s hierarchy. Liturgically, at the heart of the Church are the seven sacraments, elements of nature that, when consecrated and administered by the hierarchy, transmit grace to the Catholic faithful.
    • Baptism confers grace through consecrated water, which cleanses people from original sin, regenerates them, and incorporates them into the Church. Confirmation bestows grace through consecrated oil and the laying on of a bishop’s hands, conferring the fullness of the Holy Spirit so that the faithful are empowered to be on mission. The Eucharist, which is “the source and summit of the Christian life” (Catechism of the Catholic Church, 1324), gives grace through bread and wine, elements of nature that are transubstantiated, or transformed by God’s power, into the body and blood of Christ.
    • For Catholics who commit mortal sin (i.e., heinous, God-denying, premeditated violations of the Ten Commandments, such as homicide), Penance confers grace through certain signs and good works, thereby absolving the faithful of their sin and restoring them to salvation. For those who suffer from serious illness or are dying, the Anointing of the Sick provides grace through consecrated oil to heal them or to prepare them to face death. Holy Orders bestows grace through the laying on the bishops’ hands to ordain men to the priesthood. Matrimony confers grace upon a man and a woman who covenant together to be married.
    • By contrast, Protestants assemble in true churches that are marked by the preaching of the Word and the administration of two sacraments or ordinances, baptism and the Lord’s Supper (some Protestants add a third mark, church discipline).
  4. Salvation: Through its seven sacraments, and acting in the person of Christ, the Roman Catholic Church transmits God’s favor for salvation. Grace is infused into their recipients, transforming their character so they may work to merit eternal life. The sacraments are valid ex opere operato, that is, they instill grace simply by being administered. Their effectiveness does not depend on the priest who administers them nor on their recipients, though those who participate faithfully receive greater benefit.
    • This infusion of grace through the sacraments is key to the Catholic view of salvation. When an infant is baptized, he/she experiences initial justification, which is unmerited. With the process of salvation underway, he cooperates with God’s grace infused into him so as to engage in good works and merit eternal life. If he reaches the end of his life in a state of grace, he will ultimately be saved, though probably not immediately. Due to the stain of sin, he needs to be purged of defects. He first suffers punishment and purification in purgatory, then being perfected he may enter God’s presence in heaven.
    • Protestant theology rejects Catholic theology’s notion that “justification is not only the forgiveness of sins, but also sanctification and the renewal of the inner person [regeneration]” (Council of Trent, Decree on Justification, 7 [1547]). Rather, Protestant doctrine maintains that justification is God’s declaration that sinful people are not guilty but righteous instead. This legal pronouncement is not based on their meriting righteousness by doing good works but is due to the righteousness of Christ being imputed, or credited, to them. This doctrine of justification is one of the foundational Protestant principles.


Roman Catholic theology is characterized by both commonalities and divergences with the theologies of the other two branches of Christianity—Eastern Orthodoxy and Protestantism. Common doctrinal commitments include the Trinity, the divine nature, the revelation of God, the person of Jesus Christ, his saving work, the person and work of the Holy Spirit, the glory and depravity of human beings, the divine initiative in salvation, the community of faith, and the living hope.

In terms of its differences with Protestant theology, Catholic theology is grounded on two principles, the nature-grace interdependence and the Christ-Church interconnection. Constructed on these foundations are the Catholic doctrines of divine revelation and its interpretation, Mariology, the Church and its sacraments, and salvation. Protestant theology is grounded on two principles as well: sola Scriptura (Scripture alone) and justification by grace alone through faith alone in Christ alone for the glory of God alone.

Further Reading

  • Gregg R. Allison, Roman Catholic Theology and Practice: An Evangelical Assessment (Wheaton: Crossway, 2014)
  • Gregg Allison and Chris Castaldo, The Unfinished Reformation: What Unites and Divides Catholics and Protestants after 500 Years (Grand Rapids: Zondervan, 2016). See an Author Interview here.
  • Chris Castaldo, Holy Ground: Walking with Jesus as a Former Catholic (Grand Rapids: Zondervan, 2009)
  • Chris Castaldo, Talking to Catholics about the Gospel: A Guide for Evangelicals (Grand Rapids: Zondervan, 2015)
  • Kevin Vanhoozer, Biblical Authority after Babel: Retrieving the Solas in the Spirit of Mere Protestantism (Grand Rapids: Brazos Press, 2016)
  • Catechism of the Catholic Church
  • Gregg R. Allison, “Roman Catholics and Protestants: Commonalities and Differences,” TGC workshop (April 4, 2017)
  • Kevin DeYoung, “Protestant and Catholic: What’s the Difference,” TGC blog
  • Chris Castaldo, “Why I Left the Catholic Church,” chriscastaldo.com

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