We consider another abundant source of the evils with which the Church is afflicted at present: indifferentism. This perverse opinion is spread on all sides by the fraud of the wicked who claim that it is possible to obtain the eternal salvation of the soul by the profession of any kind of religion, as long as morality is maintained. Surely, in so clear a matter, you will drive this deadly error far from the people committed to your care. With the admonition of the apostle that ‘there is one God, one faith, one baptism’ (Eph 4:5) may those fear who contrive the notion that the safe harbor of salvation is open to persons of any religion whatever. They should consider the testimony of Christ Himself that ‘those who are not with Christ are against Him,’ (Lk 11:23) and that they disperse unhappily who do not gather with Him. Therefore ‘without a doubt, they will perish forever, unless they hold the Catholic faith whole and inviolate.’ (Symbol .s. Athanasius) Let them hear Jerome who, while the Church was torn into three parts by schism, tells us that whenever someone tried to persuade him to join his group he always exclaimed: ‘He who is for the See of Peter is for me’ (St. Jerome, epis. 57). A schismatic flatters himself falsely if he asserts that he, too, has been washed in the waters of regeneration. Indeed Augustine would reply to such a man: ‘The branch has the same form when it has been cut off from the vine; but of what profit for it is the form, if it does not live from the root?’ (St. Augustine, in psalm. contra part. Donat.) (Gregory XVI. Encyclical Mirari Vos, no. 13, August 15, 1832)

First, the council professes its belief that God Himself has made known to mankind the way in which men are to serve Him, and thus be saved in Christ and come to blessedness. We believe that this one true religion subsists in the Catholic and Apostolic Church, to which the Lord Jesus committed the duty of spreading it abroad among all men. Thus He spoke to the Apostles: ‘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, teaching them to observe all things whatsoever I have enjoined upon you’ (Mt 28: 19-20). On their part, all men are bound to seek the truth, especially in what concerns God and His Church, and to embrace the truth they come to know, and to hold fast to it. (Vatican Council II, Dignitatis humanae, no. 1, December 7, 1965)

In all of this, the Church gives voice to her awareness that with Jesus Christ she stands before the definitive word of God: he is ‘the first and the last’ (Rev 1:17). He has given creation and history their definitive meaning; and hence we are called to live in time and in God’s creation within this eschatological rhythm of the word; ‘thus the Christian dispensation, since it is the new and definitive covenant, will never pass away; and no new public revelation is to be expected before the glorious manifestation of our Lord Jesus Christ’ (cf. 1Tim 6:14; Tit 2:13) (Dei Verbum, 4). Indeed, as the Fathers noted during the Synod, the ‘uniqueness of Christianity is manifested in the event which is Jesus Christ, the culmination of revelation, the fulfilment of God’s promises and the mediator of the encounter between man and God. He who ‘has made God known’ (Jn 1:18) is the one, definitive word given to mankind’ (Prop. 4). Saint John of the Cross expresses this truth magnificently: ‘Since he has given us his Son, his only word (for he possesses no other), he spoke everything at once in this sole word – and he has no more to say… because what he spoke before to the prophets in parts, he has spoken all at once by giving us this All who is his Son. Any person questioning God or desiring some vision or revelation would be guilty not only of foolish behaviour but also of offending him, by not fixing his eyes entirely on Christ and by living with the desire for some other novelty’ (St. John of the Cross, Ascent of Mount Carmel, II, 22). (Benedict XVI. Apostolic exhortation Verbum Domini, no. 14, September 30, 2010)

The Church’s constant missionary proclamation is endangered today by relativistic theories which seek to justify religious pluralism, not only de facto but also de iure (or in principle). As a consequence, it is held that certain truths have been superseded; for example, the definitive and complete character of the revelation of Jesus Christ, the nature of Christian faith as compared with that of belief in other religions, the inspired nature of the books of Sacred Scripture, the personal unity between the Eternal Word and Jesus of Nazareth, the unity of the economy of the Incarnate Word and the Holy Spirit, the unicity and salvific universality of the mystery of Jesus Christ, the universal salvific mediation of the Church, the inseparability — while recognizing the distinction — of the kingdom of God, the kingdom of Christ, and the Church, and the subsistence of the one Church of Christ in the Catholic Church. (Congregation for the Doctrine of the Faith, Dominus Iesus, no. 4, August 6, 2000)

 171. What is the meaning of the affirmation ‘Outside the Church there is no salvation’? This means that all salvation comes from Christ, the Head, through the Church which is his body. Hence they cannot be saved who, knowing the Church as founded by Christ and necessary for salvation, would refuse to enter her or remain in her. At the same time, thanks to Christ and to his Church, those who through no fault of their own do not know the Gospel of Christ and his Church but sincerely seek God and, moved by grace, try to do his will as it is known through the dictates of conscience can attain eternal salvation. (Compendium of the Catechism of the Catholic Church, no.  171)