There is one body and one Spirit, just as you were called to the one hope of your calling,
one Lord, one faith, one baptism, one God and Father of all,
who is above all and through all and in all.
Ephesians 4, 4-5

In Protestantism, anyone who believes in Christ is considered a member of the Church that Christ founded, regardless of their denomination. The Church is seen as a spiritual body of baptized believers. On the other hand, Catholics view the Church that our Lord established as a visible and hierarchical body that consists of no independent or autonomous denominations of differing beliefs. Just being baptized is not sufficient to become a member of Christ's body. One can be removed from this body due to apostasy, heresy, schism, or excommunication from the Catholic Church, which is visibly one and apostolic since Pentecost. The Protestant paradigm suggests that the Church is invisibly united in the Holy Spirit, despite being visibly divided in the world regarding essential matters concerning faith and morals.

Now you are Christ’s Body, and individually members of it. And God has appointed in the Church, first
apostles, second prophets, third teachers, then miracles, then gifts of healings, helps, administrations,
various kinds of tongues. All are not apostles, are they? All are not prophets, are they? All are not
teachers, are they? All are not workers of miracles, are they? All do not have gifts of healings, do they?
All do not speak with tongues, do they? All do not interpret, do they? But earnestly desire the greater gifts.
1 Corinthians 12, 27-31

St. Paul uses the analogy of the Mystical Body of Christ to explain how it is a concrete unity, just like our physical bodies, with its organized different members. A unified body is made up of many parts with different functions that all contribute to maintaining its proper state. Our Lord has composed this body in such a way that there should be no division or disharmony. According to Ephesians 1:22, "He [God the Father] put all things in subjection under His [Christ’s] feet and gave Him as head over all things to the Church, which is his body, the fullness of Him who fills all in all." The body of Christ consists of many members, each of whom has a different place and function in it. These members don’t all have the same function or role. Furthermore, some spiritual gifts are greater than others, though all the members are equally dependent on each other to keep the body functioning properly.

The human body is organized in a hierarchical manner, where each subordinate function contributes equally to the unified and harmonious activity of the body. At the top of this hierarchy is Christ, who is the head of the body. The head and the members together form one body that shares a divine life. According to Ephesians 4:15-16, we are to speak the truth with love and grow up in every aspect into Christ, who is the head of the body. When each part of the body is working properly and is joined and knit together by every joint, it causes the growth of the body for building itself up in love.

The Holy Spirit is the source of life and animation for the body, and the soul of the Church. Although the Holy Spirit is invisible, the Church is not. The Church is not just a pneumatic entity, but a combination of soul and body with all its members. As Paul writes, "For we were all baptized by one Spirit to form one body, whether Jews or Gentiles, slave or free, and we were all given the one Spirit to drink" (1 Cor 12:13). The Holy Spirit is the life principle of the mystical Body of Christ and the source of unity within the Church, based on the oneness of faith. All members of the body are united with Christ by being incorporated into it through the Holy Spirit. If there is division or dissent in the Church, the cause cannot be attributed to the Holy Spirit. Dissension and division arise in the Church when some members of the body become too assertive and self-complacent, thereby infringing on the prerogatives of other members in the hierarchy. It is as if the body has been invaded by a malignant virus from an external source, namely the principality of darkness.

In Galatians 2:20, Paul speaks of the union between Christ and us in his mystical body, the Church. It is important to understand that his words are not meant to be interpreted in an individualistic sense, which is often the root of a Protestant's disinterest in joining the Catholic Church. Our union with Christ is fulfilled through our incorporation into his mystical Body, which is the Church that he founded on Peter the Rock. All members of the Church are united in faith and share one baptism in common. Jesus explains that a city set on a hill cannot be hidden, and he is referring to the Church in this instance (Mt 5:14).

The notion that the Church is an intangible, collective entity, united in the Holy Spirit, despite the existence of numerous self-governing Christian denominations with starkly different beliefs, does not align with the vision and intention of our Lord (Jn 17:11, 21, 23). Jesus entrusted Peter and, through him, the apostles with the power to "bind and loose" (Mt 16:19; 18:18). This authority to govern and teach necessitates a monolithic hierarchical structure, resulting in visible unity within the Church. The acts of binding and loosing are visible within a congregation where there is only one flock following Jesus' design (Jn 10:16).

The gifts he gave were that some would be apostles, some prophets,
some evangelists, some pastors and teachers, to equip the saints for
the work of ministry, for building up the body of Christ,
Ephesians 4, 11-12

The Church that Jesus Christ established is visibly united through its shared faith and celebration of the same sacraments. It also has a shared ecclesial hierarchy throughout the world which has been received and passed down from the apostles, whom our Lord invested with divine authority. While Jesus is the invisible Head of the Body, the Church, Peter is the visible head on earth. Each member of the visible hierarchy can be united only if the visible hierarchy is ordered to its one visible head. If the visible head of the hierarchy were a plurality of visible denominational heads in an invisible Church, then the visible hierarchies would not be essentially but only accidentally unified.

According to the Protestant notion, the Church cannot be one infallible or indefectible corporate entity that is guided by the Holy Spirit in all truth. Instead, conflicting doctrines and practices would be based on nothing more than private judgment and popular opinion in each denomination. Therefore, there could be no essential unity in the Church's teaching beyond the fundamental tenets as laid out in the early Apostles' Creed. Moreover, there could be no single and reliable teaching authority as there had been during the apostolic time and in the early Church, notably in the post-apostolic era.

In the pneumatic Church, there are numerous visible heads and separate hierarchies of different denominations that hold distinct beliefs. This creates visible disunity and a myriad of authoritative entities that impede the unity of faith. They hold opposing and unresolved theological opinions, making it difficult to determine which denominational hierarchy can rightfully claim to be protected and guided by the Holy Spirit. This dilemma has been faced by Protestants since the time of Martin Luther and is the root cause of the splintering of Protestantism, which has resulted in thousands of independent and autonomous denominations. This isn't building up the body of Christ, but rather perpetually demolishing it. It is clear that the one invisible Holy Spirit cannot be behind this mayhem that manifests itself outwardly. God cannot be the author of such confusion if the Church is to reveal the fullness of divine mysteries over time (Jn 16:12-13).

It is ironic that Protestants do not believe in the concept of Christ founding a single, visible, hierarchical Church with Peter as its head. In this concept, the apostles had to be in union with Peter for their teachings to be free from error by the guarantee of the Holy Spirit. However, every Protestant congregation has a head pastor and each mainstream denomination has its own visible hierarchy. The Church is invisible, and visible denominational churches and Protestant congregations are led by a visible head and/or hierarchy for the sake of unity in matters of faith and morals. Meanwhile, the whole of Christendom is visibly and tangibly divided in matters of faith and morals. This inconsistency, resulting from Protestant indifference, confirms the essentiality of preserving Church unity since apostolic times. Our Lord never intended to create a religious movement consisting of countless denominations. These are man-made entities that reflect a democratic political system in which freedom of speech and conviction are highly valued. However, this is not always reasonable, as the Church is actually a monarchy and kingdom.

A composite whole cannot be a single body harmoniously united without a visible hierarchy ordered to one visible head. However, the Protestant construct believes that each Protestant denomination is both a visible and an invisible body within the entire "invisible" Church. According to this belief, each denomination reflects what the Church as a whole was intended to be and, in reality, is the ancient Catholic tradition that Protestants reject. As a result, Protestants aren't practicing what they believe.

Our Lord and King, Jesus Christ, established the Church to be a unified and hierarchical visible body under one visible head who represents Him. Jesus knew that if a unified hierarchy was not in place, or if it was abandoned at some point in history, there would be nothing else to preserve unity in faith or the unity of sacraments. Paul describes the Church as a single visible body comprised of individual members who form a visible hierarchy of believers. In the Protestant paradigm, we have one invisible body comprising separate visible bodies, each with its own visible hierarchies and members under different visible heads. It is hard to believe that the one Spirit or soul animates what amounts to an incomposite body that can be divided into countless separate bodies and heads. God is not the author of confusion but of peace (1 Cor 14:33). All the churches that the apostles and their successors founded in the first century belonged to the one visible, universal (catholic) Church with Peter as its one visible head or vicar of Christ on earth.

For just as we have many members in one body and all the members do
not have the same function, so we, who are many, are one Body in Christ,
and individually members one of another.
Romans 12:4-5

In the New Testament, both Paul and John warned Christians to be cautious of false teachers and their teachings. Paul's warning was directed towards the Judaizers, and he urged the faithful to avoid them in order to maintain harmony (Rom 16:17). On the other hand, John's warning was against false teachers who were spreading Christological heresy, such as the Docetists. Although John's warning against showing hospitality to false teachers may seem harsh, it was necessary to protect the faith of the Christian community (1 Jn 4). The New Testament was written to confirm the teachings of the apostles and to dispel any confusion that might arise. The Apostolic Tradition was essential to preserving the unity of the Church and preventing it from being divided into different sects or denominations. It was important for the Church to defend the Apostolic Tradition against false teachings and teachers who lacked apostolic authority invested in them by Christ.

These dissenting sects were responsible for contentions and discord among the church’s members in various communities. Paul encouraged the church in Philippi to remain steadfast in one spirit and with one mind, working together to uphold the true faith of the gospel (Phil 1:27). He also advised the Thessalonians to stand firm and hold on to the teachings they received from the apostolic authority (2 Thess 2:15). Paul faced various challenges and false teachings that had infiltrated the Church in many regions. Thus, he prayed that all Christians would agree in one accord (Phil 2:2). When Paul appointed Timothy as bishop, he warned him about those who sought controversy and disputes by challenging the faith of believers. He reminded Timothy to safeguard and pass on the teachings handed down by the universal apostolic teaching authority of the Church (1 Tim 6; 2 Tim 2:2).

Paul acknowledged the Church as the Bride of Christ in Ephesians 5:25. This means that there is only one unified visible church, and that our Lord has only one bride, not many. Christ is the Head of one body, the Church, not countless bodies or denominations, each with its own visible head and/or hierarchy that disagrees with the other bodies of believers on some point of doctrine. Peter exhorted the faithful to have unity of spirit (1 Pet 3:8), which implies that he acknowledged the entire Church as one visible and hierarchical body. Unity of spirit and mind is impossible to achieve unless Christ established a central teaching authority on the foundation of the apostles and their valid successors in the episcopate. To avoid discord or even schism under the penalty of excommunication (2 Cor 2:17; 3:6; 5:20; 10:6; 10:8; 1 Thess 5:12-13; 2 Thess 3:14; 1 Tim 5:17; Heb 13: 7, 17; 1 Pet 5:5; 2 Pet 2:10; 1 Cor 5:3-5; 16:22; 1 Tim 1:20; Gal 1;8; Mt 18:17), this apostolic teaching authority must be respected. Through apostolic succession, this divine office has continued and will continue under the guidance and protection of the Holy Spirit to ensure the faithful transmission of tradition and doctrinal unity until Christ returns in glory (Matthew 28:16-20).

​In his vision of the Church, Daniel prophesies that people of all nations and languages shall serve God’s kingdom (Dan 7:14). This single entity is the Catholic Church. The word catholic means universal in the sense that the Church consists of all peoples of different nations and languages who, despite the global demographics of its members and different cultures, possess one mind and one spirit in faith, notwithstanding any dissension, discord, or scandal that may arise within the Church through the power of darkness, but not to the extent of its destruction. The Catholic Church has existed for almost two thousand years, outlasting all historical empires that have existed until now. It shall always exist on earth with Christ as its Head until he returns in glory. Christendom shall be perfectly united with the second coming of Christ at the end of this Messianic age.

Early Sacred Tradition

“See that ye all follow the bishop, even as Jesus Christ does the Father, and the presbytery as ye
would the apostles; and reverence the deacons, as being the institution of God. Let no man do
anything connected with the Church without the bishop. Let that be deemed a proper Eucharist,
which is [administered] either by the bishop, or by one to whom he has entrusted it. 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. It is not lawful without the bishop either to baptize or to celebrate
a love-feast; but whatsoever he shall approve of, that is also pleasing to God, so that everything
that is done may be secure and valid.”
St. Ignatius, Bishop of Antioch, Epistle to the Smyraens, 8
(c. A.D. 110)

“Those, therefore, who desert the preaching of the Church, call in question the knowledge of the
holy presbyters…It behooves us, therefore, to avoid their doctrines, and to take careful heed lest
we suffer any injury from them; but to flee to the Church, and be brought up in her bosom, and be
nourished with the Lord’s Scriptures. For the Church has been planted as a garden (paradisus) in
this world; therefore says the Spirit of God, ‘Thou mayest freely eat from every tree of the garden,’
that is, Eat ye from every Scripture of the Lord; but ye shall not eat with an uplifted mind, nor
touch any heretical discord.”
St. Irenaeus, Against Heresies, 5:20
(A.D. 189)

“Our Lord, whose precepts and admonitions we ought to observe, describing the honour of a
bishop and the order of His Church, speaks in the Gospel, and says to Peter: I say unto thee, That
thou art Peter, and upon this rock will I build my Church…Thence, through the changes of times
and successions, the ordering of bishops and the plan of the Church flow onwards; so that the
Church is founded upon the bishops, and every act of the Church is controlled by these same
rulers. Since this, then, is founded on the divine law, I marvel that some, with daring temerity,
have chosen to write to me as if they wrote in the name of the Church; when the Church is
established in the bishop and the clergy, and all who stand fast in the faith.”
St. Cyprian of Carthage, To the Lasped, Epistle 26/33
(A.D. 250)

“‘And in the last days the mountain of the house of the Lord shall be prepared on the top of the
mountains’ The house of the Lord, ‘prepared on the top of the mountains,’ is the church, according
to the declaration of the apostle, ‘Know,’ he says, ‘how thou oughtest to behave thyself in the house
of God, which is the church of the living God’ Whose foundations are on the holy mountains, for
it is built upon the foundation of the apostles and prophets. One also of these mountains was
Peter, upon which the rock the Lord promised to build his church.”
St. Basil, Commentary on Isaiah, 2:66
(A.D. 375)

He that is not with me is against me:
and he that gathers not with me scatters.
Luke 11, 23