[834] Particular Churches are fully catholic through their communion with one of them, the Church of Rome "which presides in charity."315 "For with this church, by reason of its pre-eminence, the whole Church, that is the faithful everywhere, must necessarily be in accord."316 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."317
[835] "Let us be very careful not to conceive of the universal Church as the simple sum, or . . . the more or less anomalous federation of essentially different particular churches. In the mind of the Lord the Church is universal by vocation and mission, but when she put down her roots in a variety of cultural, social, and human terrains, she takes on different external expressions and appearances in each part of the world."318 The rich variety of ecclesiastical disciplines, liturgical rites, and theological and spiritual heritages proper to the local churches "unified in a common effort, shows all the more resplendently the catholicity of the undivided Church."319
Who belongs to the Catholic Church?
[836] "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."320
[837] "Fully incorporated into the society of the Church are 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. Even though incorporated into the Church, one who does not however persevere in charity is not saved. He remains indeed in the bosom of the Church, but ‘in body’ not ‘in heart.’"321
[838] "The Church knows that she is joined in many ways to the baptized who are honored by the name of Christian, but do not profess the Catholic faith in its entirety or have not preserved unity or communion under the successor of Peter."322 Those "who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church."323 With the Orthodox Churches , this communion is so profound "that it lacks little to attain the fullness that would permit a common celebration of the Lord’s Eucharist."324