Do we believe only Catholics go to heaven?
The short answer is no. Traditionally, the answer is yes. They are both right. Let me explain. First we need to state that all salvation comes through Jesus Christ and through his one Catholic Church. Christ is the head. The body of Christ is the Church. In paragraph 846 in the Catechism of the Catholic Church (CCC), it quotes Lumen Gentium, (one of the documents of Vatican II), paragraph 14, saying, “He (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.” Any baptized Christian (baptized in “the name of the Father, and of the Son, and of the Holy Spirit) has received saving grace. We can lose that by committing a mortal sin. The next sentence in paragraph 846 reads, “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.” So if you know the Catholic Church is the one true Church started by Christ and you refuse to enter it or remain in it, then you disqualified yourself from going to heaven. However, with all of the misinformation and lack of catechesis even of cradle Catholics, I would argue this is very few people.
What about those who through no fault of their own, do not know Christ and/or His (Catholic) Church? CCC 847 again quotes Lumen Gentium (paragraph 14), “Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience – those too may achieve eternal salvation.” Now the eternal question is, is it hard or easy to “seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience”? Some people say this is easy to do and have interpreted this to mean that basically we don’t need to evangelize anymore; that everyone is saved except for maybe Hitler and Judas. This is known as Universal Salvation. Others like me have argued that this is really, really hard to do. Still others have taken up some position in the middle. I think it is really hard to seek God with a sincere heart and to follow my conscience constantly and ardently. I think it really hard for anyone to seek God with a sincere heart and to do God’s will as they understand it to be. But this is what is required for a non-Catholic to do these things and thus get to heaven. I know I, time and time again, do not seek God and disobey my conscience, the voice of the Holy Spirit. Thankfully I am Catholic. Thankfully I have access to the Sacrament of Reconciliation. Thankfully I have access to other Sacraments, especially the Eucharist (See John 6:53-54). Again, I think it is hard to “seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience,” So it is hard, but not impossible for a non-Catholic to get to heaven. Therefore, I agree with the end of CCC 848, which reads, “the Church still has the obligation and also the sacred right to evangelize all men.”