At the most fundamental level, I believe the one thing that ultimately divides Catholics and Protestants is the issue of authority and where that lies in terms of scripture, tradition, and general church beliefs and organization. This is fundamental because from it springs forth all other problems/hindrances that seem to arise. Ultimately, authority rests in God. All of creation must answer and must be under his authority. The Lord Himself speaks at the end of the gospel of Matthew that "All power in heaven and on earth has been given to me. 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 that I have commanded you." (Matthew 28:18-20).
As Catholics we render authority within and through the Church, just as it has been from the beginning. Remember what Christ said to Peter, "You are Rock and upon this Rock, I will build my Church." (Matthew 16:16). Who's Church? HIS, Church. Where do we go when we have problem within our believing community, not just to scripture. If you can't discern something from scripture, you appeal to the Church, which is the pillar and bulwark of truth (1 Timothy 3:15). God established a Church. That's clear. What is disputed is how much authority this Church actually has. Is the Church a product of the scriptures or are the scriptures the product of the Church? This Church has the power to bind and to loose. This Church has the power to affect salvation. This Church has the authority to determine the canon of Scripture. Even by appealing to scripture, our Protestant brothers and sisters are relying on the authority of the early Catholic councils as to what exactly constitutes the canon of scripture. (However, due to the unfortunate Revolt of the 16th century, most Protestants do not have the complete Bible.)
This authority goes beyond what even the canon of scripture is. Based on the fact that the individual believer can have a "burning in his heart" as to the "true" meaning of scripture, someone can twist it to conform to anything that they want it to. The rubrics of interpretation are thrown out the window without the proper authority to give you guidelines on how to interpret the passages of scripture. I seem to remember a certain eunuch in Acts that needed someone to determine what the scriptures mean (see Acts 8:30-38). When trying to show how and where the Church derives some of it's teachings and practices from scripture to a non-Catholic, verses seem to be thrown back that in essence have nothing to do with the matter being discussed. Of course, you have no idea what they will use it to support or negate because the individual has essentially become his own pope. Problems arise in the fact that in determining what is “essential” and “orthodox” are left up to the individual believer in this vacuum of authority. In today’s individualistic society this is no more apparent than in the seemingly endless divisions of Protestantism.
There seems to be an unnecessary dichotomy that arises when non-Catholics look at authority. They make a distinction between authority of the Church and authority of scripture. When in reality, they are complementary and there is no reason that they both cannot have authority, albeit different from each other. Where does authority of anything relating to Christ derive it's nature from? God the Father through God the Son given to the Apostles and those they pass the authority on to. The authority of the apostles sets apart what is orthodox and not heresy. They teach "all the Christ has commanded." We have, on God's own authority, the promise that "the Spirit will lead us into all truth." That is a future tense. It is a teaching authority that has it's blessing from God Himself.
So how do we know what to believe? Who has the authority to guide someone to what to believe and how do they know that that is the correct way? I think that that authority should ultimately rest in something or someone. We know as Catholics that the authority rests in Someone and that that Someone promised that He would be with us until the end. Not only that, but he would also send the Spirit to guide the Church into all truth. Now since Jesus is the ultimate Truth, then we have confidence in the fact that he can follow through on his promises and that deriving his authority from God the Father himself, he in turn is sharing that authority with the church and with us. The authority rests in the divinely established and mandated church. Because of that promise, the Church is still in existence and it is the Catholic Church. The fullness of the Christian faith rests with her because of the authority she was given by God to spread his message.
As Christians of the 21st century, we have a unique perspective of looking back not only through 2000 years of Church history but also the effects of said history and the beauty and depth of our history. Both sides can help each other to see the common ground that does exist and discuss at the most fundamental level what authority is and what it constitutes. People today do not like the concept of authority or heirarchical structures. Regardless, I think that a full quote from St. Cyprian is appropriate:
“The Lord says to Peter: ‘I say to you,’ He says, ‘that you are Peter, and upon this rock I will build my Church, and the gates of hell will not overcome it. And to you I will give the keys of the kingdom of heaven: and whatever things you bind on earth shall be bound also in heaven, and whatever you loose on earth, they shall be loosed also in heaven.’ And again He says to him after His resurrection: ‘Feed my sheep.’ On him He builds the Church, and to him He gives the command to feed the sheep; and although He assigns a like power to all the Apostles, yet He founded a single chair, and He established by His own authority a source and an intrinsic reason for that unity. Indeed, the others were that also which Peter was; but a primacy is given to Peter, whereby it is made clear that there is but one Church and one chair. So too, all are shepherds, and the flock is shown to be one, fed by all the Apostles in single-minded accord. If someone does not hold fast to this unity of Peter, can he imagine that he still holds the faith? If he desert the chair of Peter upon whom the Church was built, can he still be confident that he is in the Church?”
--St. Cyprian, AD 251
