CATHOLIC CHURCH - The Church is catholic because of its relation to God, Christ, and the Holy Spirit. The word catholic means full, complete, whole, with nothing lacking. God alone is full and total reality; in God alone is there nothing lacking.
Sometimes the catholicity of the Church is understood in terms of the Church’s universality throughout time and space. While it is true that the Church is universal—for all men at all times and in all places—this universality is not the real meaning of the term “catholic” when it is used to define the Church. The term “catholic” as originally used to define the Church (as early as the first decades of the second century) was a definition of quality rather than quantity. Calling the Church catholic means to define how it is, namely, full and complete, all-embracing, and with nothing lacking.
Even before the Church was spread over the world, it was defined as catholic. The original Jerusalem Church of the apostles, or the early city-churches of Antioch, Ephesus, Corinth, or Rome, were catholic. These churches were catholic—as is each and every Orthodox church today—because nothing essential was lacking for them to be the genuine Church of Christ. God Himself is fully revealed and present in each church through Christ and the Holy Spirit, acting in the local community of believers with its apostolic doctrine, ministry (hierarchy), and sacraments, thus requiring nothing to be added to it in order for it to participate fully in the Kingdom of God.
To believe in the Church as catholic, therefore, is to express the conviction that the fullness of God is present in the Church and that nothing of the “abundant life” that Christ gives to the world in the Spirit is lacking to it (Jn 10:10). It is to confess exactly that the Church is indeed “the fullness of him who fills all in all” (Eph 1:23; also Col 2:10).