At a home gathering in New York City hosted by my sister and attended by her friends from a denominational Christian community, a guest asked me politely why I identified myself as a Catholic and not as a Christian.
Just as politely I assured her that I felt just as honored and blessed to be called a Christian as the early Church faithful whose Christian identity was first confirmed publicly in Antioch (cf. Acts 11:26).
Then I drew her attention to the “mystery of Christ” that God revealed to St. Paul and the holy apostles:
When you read this you can understand my insight into the mystery of Christ, which… has now been revealed to his holy apostles and prophets by the Spirit, that the Gentiles are coheirs, members of the same body, and co-partners in the promise in Christ Jesus through the gospel…To me, the very least of all the holy ones, this grace was given, to preach to the Gentiles the inscrutable riches of Christ… (Eph. 3:4-8).
The same realization of the universality or catholicity of the Christian faith hit St. Peter like a rock when he received a mysterious vision in which he was asked to eat things that were considered profane under the Mosaic law (cf. Acts 10:9-16). When everything finally sank in, he confided his newfound understanding to the uncircumcised Gentiles whom he subsequently baptised:
In truth, I see that God shows no partiality. Rather, in every nation whoever fears him and acts uprightly is acceptable to him. You know the word (that) he sent to the Israelites as he proclaimed peace through Jesus Christ, who is Lord of all… (Acts 10:34-36).
Catholicity was the reason for the decision of the Council of Jerusalem to avoid “placing on the shoulders of the [Gentiles] a yoke that neither our ancestors nor we have been able to bear,” namely the burden of observing the Mosaic law, particularly the requirement of circumcision (Acts 16:10).
It was for the fulfillment of the catholicity of his Church that Jesus on his Ascension into glory mandated his disciples to “go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the holy Spirit” (Mt. 28:19) – a mission faithfully and successfully carried out by the Church in her history of over 2,000 years; a mission so prominent to her identity and intrinsic to the core of her being that the Church Fathers had made a point of including it as one of the four marks of the Church in the Creeds: I believe in one, holy, catholic, and apostolic Church.
The term “Catholic Church” was already in use as early as St. Ignatius of Antioch (d. 108 A.D.), one of the five Apostolic Fathers (the earliest authoritative group of the Church Fathers): “Wherever the bishop appears, there let the people be; as wherever Jesus Christ is, there is the Catholic Church” (St. Ignatius of Antioch, Letter to the Smyrnaeans 8).
Without catholicity, without the firm belief in the unicity (as in Christ being the only Savior and his Church the only house of God that brings salvation) and salvific universality of the mystery of Christ, the Christian Church would have been just a sect of Judaism, restricted in many ways by local customs and one nation’s history and traditions.