Et unam sanctam catholicam et apostolicam Ecclesiam
“I believe in one, holy, catholic and apostolic Church,” is a key line in the Nicene Creed. This part was appended at the First Council of Constantinople (381) to the earlier Creed of Nicaea (325). While the earlier creed responded to false teachings about Christ, particularly Arian Controversy, this later addition clarified the role of the Holy Spirit and the life of the Church. It affirms that through the Spirit, believers share in God’s life—a gift that brings salvation, eternal life, and shapes the life of the Church.
The four words—one, holy, catholic, and apostolic—are often called the “marks of the Church.” They help us understand what the Church is and what it is meant to be.
Oneness: Unity in Christ
The Church is called “one,” but what does that mean? From the beginning, Christian believers did not always live in perfect harmony. Yet, as Paul the Apostle wrote, believers were already one in Christ (Gal. 3:28), despite conflicts between Jews and Greeks, slaves and free people, and males and females.
Early Christian leaders like Irenaeus explained that this unity is seen in a common faith, sacraments, and ministry as the marks of unity. Writing against groups like the Gnostics, he argued that unity is not based on private ideas or secret knowledge, but on the common life of the Church.
More deeply, united is rooted in God Himself. Irenaeus famously said this: “For where the Church is, there is the Spirit of God; and where the Spirit of God is, there is the Church, and every kind of grace; but the Spirit is truth” (Against Heresies 3.24.1).
The Bible reflects this clearly. In Eph. 4:4–6, Paul speaks of “one body and one Spirit… one Lord, one faith, one baptism, one God and Father of all.” This unity mirrors the unity within God Himself. In Jn. 17:20-21, Jesus prays that His followers may be one, just as He and the Father are one. Through the Holy Spirit, believers share in this divine unity.
The Church’s oneness is therefore both invisible and visible. It is invisible in that all believers, across time and space, belong to Christ. It is visible in shared doctrine, sacraments, and mutual recognition.
At the same time, unity does not mean uniformity, Diversity has always existed in the Church. Differences in cultures, worship styles, and church structures do not necessarily destroy unity, as long as the core faith in Christ remains intact.
Today, different Christian traditions understand unity in different ways. Some emphasise spiritual unity, while others stress visible unity through structures and leadership. Yet, all affirm that the Church is one. In a world where Christianity is divided into many groups, this mark calls believers to humility, repentance, and a renewed effort to seek unity in Christ without demanding uniformity in practice.
Holiness: Sanctified by Grace
The Church is called “holy” because God is holy. God has chosen His people, set them apart, and given them a share in His holiness (Lev. 19:2; 1 Pet. 1:15–16).
Through Christ, believers are declared holy (justification). As Paul says in Eph. 5:25–27, Christ gave Himself for the Church to make her holy and blameless. In this sense, holiness is a gift.
However, the Church on earth is not perfect. It is a mixed community, as described in parables about wheat and weeds (Matt. 13:24-43) or good fish and bad fish (13:47-50). St. Augustine of Hippo addressed this problem in The City of God. While Christians are called “saints,” they are still growing into that calling.
Holiness, therefore, is also a process. Believers grow in holiness over time through the work of the Holy Spirit (sanctification). This growth happens through prayer, reading Scripture, participating in the life of the Church, and living in obedience to God.
Basil the Great (c. 330–379 AD) beautifully described: “The soul’s physician heals willingly those who have recourse to him” (Moralia, Rule 12). The more we allow God’s grace to work in us, the more we reflect His holiness. The Church is holy because God is at work within it. Its mission is to share this holiness with the world—not by being perfect, but by being transformed by God’s grace.
Catholicity: A Universal Community
The word “catholic” comes from the Greek word katholikos, meaning “according to the whole.” It describes the Church as a worldwide community that includes people from every nation, culture, and generation.
Although the word itself does not appear in the New Testament, the idea is present throughout. St. Ignatius of Antioch was one of the first to use the term katholikos to describe the universal body of believers gathered around Christ (c. 110 AD): “Wherever the bishop shall appear, there let the multitude [of the people] also be; even as, wherever Jesus Christ is, there is the Catholic Church” (katholikē ekklēsia), (Letter to the Smyrnaeans 8.2).
Jesus commanded His followers to make disciples of all nations (Matt. 28:19). This universal mission became visible at Pentecost (Acts 2), when people from many parts of the world heard the message of Christ in their own languages.
It is important to understand that the word “catholic” in the Creed does not refer exclusively to the Roman Catholic Church. The Creed was written long before later divisions developed. Hene, “catholic” simply means universal Church that holds the apostolic faith across the world.
Catholicity reminds us that the Church must avoid being narrow or limited to one culture. It welcomes people from every background, as described in Rev. 7:9—a great multitude from every nation and language.
At the same time, catholicity does not mean accepting everything without discernment. The Church must remain faithful to the truth of the gospel while embracing cultural diversity. It stands between two dangers: being too narrow on the one hand, and losing its identity on the other.
Apostolicity: Faithful to the Apostles
The Church is “apostolic” because it is built upon the foundation of the apostles—the first witnesses of Jesus Christ. As Eph. 2:20 says, the Church is built on the foundation of the apostles and prophets, with Christ Jesus himself as the cornerstone.
From the beginning, Christian devoted themselves to apostolic teaching, fellowship, the breaking of bread, and prayer (Acts 2:42). This pattern continues to shape the life of the Church.
Leaders like Irenaeus strongly emphasises that true teaching comes from the apostles and has been passed down faithfully:
“We have learned from none others the plan of our salvation than from those through whom the Gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith” (Against Heresies, 3.1.1).
He argued that the true Church preserved the teaching received from the apostles, while false groups like the Gnostics depart from it.
Apostolicity means remaining faithful to the message of the apostles, as recorded in Scripture. It also involves continuity across generations, as the Church hands down this faith through teaching, worship, and mission.
The apostles not only taught the gospel but also lived it. They discipled others, wrote Scripture, and gave their lives in service. Their work continues through those who teach and lead the Church today.
Of course, human leaders are not perfect. They may fail. Yet believing in an apostolic Church means trusting that Christ continues to work through human weakness to accomplish His purposes.
Conclusion
These four marks—one, holy, catholic, and apostolic—are deeply connected:
- Oneness without holiness risks compromise.
- Holiness without catholicity can become isolation.
- Catholicity without apostolicity can lead to doctrinal dilution.
- Apostolicity without oneness can result in fragmentation.
Together, they describe the Church as rooted in the life of the Triune God—Father, Son, and Holy Spirit.
The Church shares in God’s life and is sustained by the Holy Spirit. It is called to live out this identity in the world through faith, love, and witness. The full reality of these marks will only be seen when Christ returns. Until that time, the Church lives in hope, striving to embody the unity, holiness, universality, and faithfulness that the Creed proclaims.
Suggested Reading:
Barron, Robert. What Christians Believe: Understanding the Nicene Creed. Word on Fire, 2025.
Cary, Phillip Cary. The Nicene Creed: An Introduction. Bellingham, WA: Lexham Press, 2023.
Connor, Lombard R. The Nicene Creed and the Arian Heresy: Early Church Fathers and the Early Church. Independently published, 2025.
Keating, Daniel A., and Ortiz, Jared. The Nicene Creed: A Scriptural, Historical, and Theological Commentary. Grand Rapids, MI: Baker Academic, 2024.
