The following is a infallible Catholic dogma:
Pope Eugene IV, in the Bull Cantate Domino, 1441, who proclaimed
ex cathedra: “The Most Holy Roman Church firmly believes, professes and preaches that none of those existing outside the Catholic Church, not only pagans, also Jews, heretics, and schismatics can ever be partakers of eternal life, but that they are to go into the eternal fire ‘which was prepared for the devil and his angels’ (Mt. 25:41) unless before death they are joined with Her… No one, let his almsgiving be as great as it may, no one, even if he pour out his blood for the Name of Christ can be saved unless they abide within the bosom and unity of the Catholic Church.”
The following is the consistent teaching of the Church from the earliest years of the Church
St. Augustine (354-430), Bishop and Doctor of the Church: “No man can find salvation except in the Catholic Church. Outside the Catholic Church one can have everything except salvation. One can have honor, one can have sacraments, one can sing alleluia, one can answer amen, one can have faith in the Name of the Father and the Son and of the Holy Ghost, and preach it too, but never can one find salvation except in the Catholic Church.”
St. Fulgentius (468-533), Bishop: “Most firmly hold and never doubt that not only pagans, but also Jews, all heretics, and all schismatics who finish this life outside of the Catholic Church, will go into eternal fire prepared for the devil and his angels.”
Pope St. Gregory the Great (590-604): “The holy universal Church teaches that it is not possible to worship God truly except in Her and asserts that all who are outside of Her will not be saved.”
St. Francis of Assisi (1182-1226): “All who have not believed that Jesus Christ was really the Son of God are doomed. Also, all who see the Sacrement of the Body of Christ and do not believe it is really the most holy Body and Blood of the Lord . . . these also are doomed!”
St. Thomas Aquinas (1226-1274), the Angelic Doctor: There is no entering into salvation outside the Catholic Church, just as in the time of the Flood there was not salvation outside the Ark, which denotes the Church."
St. Louis Marie de Montfort (1673-1716): “There is no salvation outside the Caholic Church. Anyone who resists this truth perishes.”
St. Robert Bellarmine (1542-1621), Bishop and Doctor of the Church: “Outside the Church there is no salvation…therefore in the symbol (Apostles Creed) we join together the Church with the remission of sins: 'I believe in the Holy Catholic Church, the communion of saints, the forgiveness of sins”…For this reason the Church is compared to the Ark of Noah, because just as during the deluge, everyone perished who was not in the ark, so now those perish who are not in the Church." St. Alphonsus Maria de Liguori (1696-1787), Bishop and Doctor of the Church: “All the misfortunes of unbelievers spring from too great an attachment to the things of life. This sickness of heart weakens and darkens the understanding, and leads to eternal ruin. If they would try to heal their hearts by purging them of their vices, they would soon receive light, which would show them the necessity of joining the Catholic Church, where alone is salvation. We should constantly thank the Lord for having granted us the gift of the true Faith, by associating us with the children of the Holy Catholic Church … How many are the infidels, heretics, and schismatics who do not enjoy the happiness of the true Faith! Earth is full of them and they are all lost!”