The interpretation of Extra Ecclesiam Nulla Salus has been a controversy for a long time in the Church. This debate has already raged on for centuries.
To believe that only Catholics go to heaven, no matter what, has been condemned as a heresy. This is called Feeneyism.
There are several levels on which I must object.
Firstly, the Catechism of the Catholic Church (No. 776) Reads:
As sacrament, the Church is Christ’s instrument. She is taken up by Him also as the instrument for the salvation of all, the universal sacrament of salvation, by which Christ is at once manifesting and actualizing the mystery of God’s love for men. The Church is the visible plan of God’s love for humanity, because God desires that the whole human race may become one People of God, form one Body of Christ, and be built up into one Temple of the Holy Spirit. Discussion: There are two principal errors when it comes to the Church’s teaching on extra ecclesiam nulla salus. Some reject this teaching as both incorrect and arrogant. Others interpret this statement to condemn all those who are not visibly united to the Roman Catholic Church. To properly understand this teaching, we must examine it within the context of divine Revelation and Church history. This examination will reveal that the phrase was not formulated to express who would go to heaven and who would go to hell, for only God will judge that. Rather, the phrase expresses an understanding of the Church in relation to her role in the salvation of the world.
Furthermore, Pope Pius XII reaffirmed that those who are ignorant of the Gospel, but not by their own will have a chance at salvation.
The major problem with this comes from how we interpret “by their own will.”
To employ simile, trying to attain salvation outside the formal fold of the Church is like cleaning a loaded gun: everything may workout, but on the other hand, you may shoot yourself in the head.