I typed up a post on this very subject just five months ago, answering this question from an historical document. I’ve thought about it some more, and have a much cleaner answer to the question.
And, as always, please remember that Catholic Christianity is not limited to the Roman Catholics. There are other Catholics out here too!
Question & Answer Introduction
Q: So what is Catholicism or Catholic Christianity?
A: It’s a faith & religion centered around Jesus.
Q: Oh, very funny Matt, all Christians are centered around Jesus. It’s in the very name, Christians.
A: Yup! And that’s the most important starting point, Catholicism is Christianity. Some folks out there still think Catholics aren’t Christians.
Q: So… what distinguishes Catholic Christianity from non-Catholic?
A: It’s all in how we center around Jesus.
Q: This sounds complicated.
A: Not at all, I can break it down into three categories: doctrine, worship, and community.
Jesus at the center of our doctrine
Jesus said that he is the way and the truth and the life. John described Jesus as the light that was coming into the world. The Holy Spirit was promised to lead us into all truth by reminding God’s people of Christ. In short: Jesus is the primary source of all our knowledge of God. Being fully God, he has perfect knowledge of God. Being fully human, he is perfectly capable of communicating God in a way that we can understand. Christians, therefore, sit at the feet of Christ to be instructed in knowledge of God, ourselves, and our salvation (and so on).
But of course, Jesus isn’t walking the earth at present, so how do we learn Christian doctrine from him? There are lots of resources: creeds, councils, academic theological study, personal experiences of God, but at the center of all this is the Bible. The Bible is the icon (image) of the Word of God (Jesus). Due to its double authorship including God along with the human writers, the Bible is supernaturally apt for revealing Christ to us in an authoritative way that nothing else can match. We have creeds, councils, teachers, and experiences that help shape our understanding of what the Scriptures say, and every Christian group has a different way of balancing these things, even those who fall under the banner of Catholic. But at the heart of it all is always the Sacred Scriptures – the Bible.
Jesus at the center of our worship
To say that Jesus is at the center of our worship does not mean that we worship Jesus exclusively. Rather, Catholic Christianity worships God in Trinity: Father, Son, and Holy Spirit. By putting Jesus at the center of our worship, I mean that he is the defining leader of our worship as well as the one who defines the event that centers Christian worship. Just as the Passover set the stage for the Israelite community’s freedom from Egypt, and thus became the center of Israelite worship, so too does Christ on the Cross set the stage for the Christian community’s freedom from Satan, and thus became the center of Christian worship. Since Jesus was himself that sacrifice as well as the high priest who offered himself, he is both the event that we reach back to in worship, as well as our worship leader.
Knowing that he would not be among us visibly in person through this age, Jesus instituted the worship practice that apprehends his sacrifice on the Cross for us: the sacrament of Holy Communion. By setting his sacrificial death into the context of the Passover, and by naming his Body and Blood during the Passover meal, he made a spiritual link between the power of his death & resurrection and the celebration of the Christian Passover meal known to us as Eucharist or Communion. Just as the Passover meal celebrated and re-enacted the Israelite salvation from Egypt, the Eucharist celebrates and re-enacts our salvation from sin. And so we receive his life and salvation, and give thanks – the very definition of the word eucharist.
Jesus at the center of our community
Finally, Jesus is at the center of the Catholic community – we gather around him to lead us and teach us and care for us. He is the “shepherd and bishop of our souls,” as Peter wrote, not to mention our Lord and King. No Christian contends that. What divides Christians today is the question of how the spiritual authority of Jesus exists among the leaders of the Church in his visible absence. As promised in Matthew 16 & 18 and enacted in John 20 we see Jesus clearly passing on authority to his apostles. There is a succession of authority there; but what comes next?
Catholic Christianity, as universally attested in the first millennium of the Church, is led by Bishops. Just as Jesus passed his authority on to his apostles, the apostles then passed on their authority to their successors. Those successors then appoint the next generation of leaders, and so on spreading throughout the world through the ages. By the year 200 the terminology had settled: these leaders are called bishops. The word comes from the Greek episkopos and is found in several places throughout the New Testament, commonly translated today as “overseer.” Certainly other Christians have leaders, though usually they don’t use the word bishop. What identifies Catholic leadership is this historically consistent reception of leadership, rather than one of the (many) modern interpretations of biblical leadership.
Final notes of contrast
So Catholicism is marked by the centrality of Jesus, represented by the Bible for our teaching, the Eucharist for our worship, and Bishops for our spiritual leaders.
Non-Catholics, then, employ other means of centering their doctrine, worship, and communities around Jesus. Classical Protestantism tends to attempt to put the Bible at the center of their worship, resulting in the elevation of the sermon as the focal point of Sunday worship. The radical reformers attempted to put the Bible at the center of their community leadership, resulting in the undermining of significant pastoral leadership in many cases. Pentecostal or Charismatic Christians tend to put experiences of the Holy Spirit at the center of their worship. Congregationalism is a tradition that replaces Bishops with a form of democratic leadership. All of these are attempts to put Jesus at the center.
Some of these other traditions have interpreted history to see their view in the practice of the Early Church (such as the Presbyterian rejection of the distinction between priests/elders and bishops), but many simply ignore the early history of the Church (such as the many who push the Eucharist to the fringe of their worship tradition).
Lastly, this triple representation of Jesus (in Scripture, Eucharist, and Bishop) lays the groundwork for what Catholics call the “sacramental reality of the Church.” A sacrament is “a means of grace;” it’s a way that God communicates himself through the use of his creation. The Bible, the Eucharist, and the Bishop are sacramental in nature – by their very existence (and moreso when used properly) they communicate God and his Truth to the world. Without them, the Church is not communicating God to the world. Thus when some Christians do away with one or two of these things, or redefine them according to their own preferences, they diminish the clarity of the Gospel, the proclamation of who God is. That’s why Catholics describe non-Catholics as lacking the fullness of the ministry of the Church. A non-Catholic Christian is still a Christian, but is missing out on one or two thirds of the Church’s identity and ministry.