It is generally acknowledged that the word Catholic Church first appears in the writings of the apostolic father, St. Ignatius of Antioch, in his Letter To the Smyrnaeans in the year 110 A.D. The context of the use of the term is as follows: Wherever the bishop appears, let the people be there; just as wherever Jesus Christ is, there is the Catholic Church. As the Catechism of the Catholic Church (#830) states: The word catholic means universal, in the sense of according to the totality or in keeping with the whole. The Church is catholic in a double sense: First, the Church is catholic because Christ is present in her. Where there is Christ Jesus, there is the Catholic Church (St. Ignatius). In her subsists the fullness of Christ's body united with its head; this implies that she receives from him the fullness of the means of salvation which he has willed: correct and complete confession of faith, full sacramental life, and ordained ministry in apostolic succession. The Church was, in this fundamental sense, catholic on the day of Pentecost and will always be so until the day of the Parousia.
Secondly, the Church is catholic (#831) because she has been sent out by Christ on a mission to the whole of the human race. Wherever the faithful gather united under their pastors the universal Church is made present. Hence, in Sacramento the universal or "Catholic" Church gathers and celebrates, teaches and serves. As the Catechism (#834) states: Particular Churches [i.e., dioceses] are fully catholic through their communion with one of them, the Church of Rome which presides in charity. For with this church, by reason of its pre-eminence, the whole Church, that is the faithful everywhere, must necessarily be in accord. Indeed, from the incarnate Word's descent to us, all Christian churches everywhere have held and hold the great Church that is here [at Rome] to be their only basis and foundation since, according to the Savior's promise, the gates of hell have never prevailed against her. It is through union with Rome--obedience to the bishop of Rome, the pope--that full incorporation into the church that Christ instituted upon "Peter" is guaranteed. The Holy Father is the guarantor of unity, and it is through faithful obedience and union with his office and his teaching that the church's unity, holiness, catholicity, and apostolicity are guaranteed.
The Catechism clarifies the question of who belongs to the Catholic Church: "All men are called to this catholic unity of the People of God....And to it, in different ways, belong or are ordered: the Catholic faithful, others who believe in Christ, and finally all mankind, called by God's grace to salvation" (#836). There are certain criteria which determine full incorporation into the one church instituted by Jesus Christ: those, who possessing the Spirit of Christ, accept all the means of salvation given to the church together with her entire organization; and who by the bonds constituted by the profession of faith, the sacraments, ecclesiastical government, and communion--are joined in the visible structure of the Church of Christ who rules her through the Supreme Pontiff and the bishops (#837).
However, it is to be soberly remembered that simply being a member of the Catholic Church is no guarantee of salvation. "When much has been given a man, much will be required of him. More will be asked of a man to whom more has been entrusted" (Luke 12:48b). In the Catholic Church we have all seven of the sacraments, and we have been given the fullness of divine Revelation, since we have not only Scripture tradition as well; and the church's magisterium, which is necessary to authentically and authoritatively interpret the Word of God, whether written in the Bible or handed down by the apostolic tradition. Catholics are thus required to live a life much more in accord with the Spirit of Christ. The gift is great, but so too is the responsibility.
The church has a real relationship with all mankind, for all are called to the perfection of charity, and that can be achieved only by using the full means the Lord has given us. All Christians, Jews, Muslims, and the entire human race are our brothers and sisters, and they are called to the fullness of the church's blessings. It would be a false ecumenism which did not desire ardently that all men would enter into the fullness of Catholic unity in the church instituted by Jesus the Christ.
All salvation comes from Jesus Christ, the head of his mystical body, through his body, the church. Hence, there is indeed no salvation outside the church. The Second Vatican Council teaches clearly that the church is necessary for salvation: Jesus himself explicitly asserted the necessity of faith and Baptism, and thereby affirmed at the same time the necessity of the Church which men enter through Baptism as through a door. Hence they could not be saved who, knowing that the Catholic Church was founded as necessary by God through Christ, would refuse either to enter it or to remain in it (Vatican II, Lumen gentium, 14; Catechism #846). The Catechism makes it clear, however, that this affirmation is not aimed at those who, through no fault of their own, do not know Christ and his church (#847). "Although in ways known to himself God can lead those who, through no fault of their own, are ignorant of the Gospel, to that faith without which it is impossible to please him, the Church still has the obligation and also the sacred right to evangelize all men" (Vatican II, Ad gentes, 7; Catechism #848). We know that God can use extraordinary means to save any person, but the only ordinary means of salvation we know of is through the church, the "universal sacrament of salvation."
Hence, missionary activity is an absolute requirement of the church's catholicity: Having been divinely sent to the nations that she might be the universal sacrament of salvation, the church, in obedience to the command of her founder and because it is demanded by her own essential universality, strives to preach the Gospel to all men" (Vatican II, Ad gentes, 1; Catechism #849). Having "put on the mind of Christ," being filled with the Holy Spirit, the protagonist and principal agent of the whole of the Church's mission, each and every one of us in the Catholic Church should long for the day when there is "one Shepherd and one flock." We should desire most sincerely that all persons have what we have: the full means of salvation--all seven sacraments, celebrated licitly and validly, as well as the fullness of divine Revelation. How can we be content until every one of our brothers and sisters believe what we believe and have Jesus himself in the Eucharist, which is the source, the center, and the summit of Christian life. May the God who is One grant us this gift of his universal love for humankind!