So I am a Protestant considering doing RCIA in the fall and when I talked to the priest at the parish I am attending he said that Catholicism is the “fullness of the Christian Faith.” I’ve heard this phrase from other Catholics as well but I am not sure what it means. Is it the same as “the fullness of Truth”?
Catechism of the Catholic Church:
868 The Church is catholic: she proclaims the fullness of the faith. She bears in herself and administers the totality of the means of salvation. She is sent out to all peoples. She speaks to all men. She encompasses all times. She is “missionary of her very nature”
Yes, it would be comparable to the expression “fullness of truth.”
Essentially what it means is that other Christian groups are not in error in every single thing they believe and teach but that they are in error on some things.
For example, many Protestant groups share the Catholic understanding of baptism but then they are in error about the other sacraments. While they have one sacrament, the “fullness” of sacramental life is found in the Catholic Church.
Another example would be the Bible. Catholics and Protestants share 39 books of the Old Testament, but Catholics have an additional 7. Thus while these other Christian groups have some of the Bible, the “fullness” of the Bible is found in the Catholic Church.
We do indeed have many beliefs in common with various other Christian faith communities but the differences are important. So others may have some truth in their beliefs and teachings, they just don’t have the fullness of the Christian faith/truth.