I recently attended a Mass in which the celebrant’s homily addressed what is in some circles a fairly thorny issue: the relationship between Scripture (the Bible) and Tradition.
According to Catholicism, “Tradition” with a capital “T” is to be distinguished from “tradition” with a lowercase “t”. Tradition is permanent, unchangeable, and given to the mind of the church by Christ; tradition is contingent, malleable, and can be forsaken or created at a whim. Tradition includes dogmas, such as the Trinity and the existence of Seven Sacraments; tradition includes things such as the specific application of certain liturgical practices (for example, do we pray the Mass in Latin or in the vernacular?).
It is a claim of the Catholic Church that Christ handed on something called “the deposit of faith” to the Twelve Apostles. Although some Christians have been called “apostles” since the Twelve, not all “apostles” were entrusted with authority by the Lord Jesus. Catholicism sees the original apostles as having a unique role that is continued by their successors, namely, the Bishops that they ordained.
“The deposit of faith” is a biblical phrase (2 Timothy 1:14), by the way. Catholicism is surprisingly biblical if one is willing to give it a fair hearing.
What does this deposit of faith contain? It contains the entirety of the Christian revelation. This is why “even if an angel should preach another gospel”, the Catholic Christian cannot entertain him. There is nothing new that can possibly be added to the deposit of faith; the deposit of faith can only be understood on a deeper level. This in essence is the Catholic Church’s self-understanding. The teaching authority of the Catholic Church — the Pope and the Bishops in communion with him throughout time — can only interpret and define the dogmas of the deposit of faith; they cannot invent or create them.
For example, at the Council of Nicea, the teaching authority of the Catholic Church (the Bishops in communion with the Pope) did not invent the doctrine of the Incarnation as the Nicene council proclaimed it. Rather, the Bishops defined the faith that the apostles already had in words that were less ambiguous than those of the Bible. The theologians of Arius, after all, were also masters of biblical exegesis. The Bible can be used to support almost anything, and this is why the Catholic Church does not believe that “Sola Scriptura” can possibly be a defining point for Christian orthodoxy. In order to define orthodoxy in such a way that even a layman can understand it, another teaching authority is necessary. So the story goes as told by the Roman Church.
How does this relate to Scripture and Tradition? It clarifies that Scripture and Tradition are not as different as one might think. Rather, they flow from the same source — the deposit of faith given by Christ to the authorities He appointed (the Apostles) and, in turn, the authorities that the Apostles appointed “by the laying on of hands (2 Tim. 1:6), the Bishops. Scripture, Tradition, and the Bishops in communion with the Pope are intimately bound one to another. If any piece of this link were missing, the entire structure would collapse into anarchy and infinite schism.
One point that drives this home is the need to canonize the Bible. One of the ironic problems associated with Sola Scriptura (“Bible alone”) is that the Bible alone cannot tell a person which books belong in the Bible. Martin Luther and John Calvin can tell you which books they think should be in the Bible; but how could one be sure that they are right? For confidence in the canon of Scripture, one must ultimately look to something other than Scripture.
The same is true of the meaning of Scripture. Scripture can tell you, “Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you” (John 6:53), but ultimately, to know what that means, someone else must interpret for you.
We see a poignant example of this process in the Bible itself. In the book of Acts, an Ethiopian eunuch was reading the book of Isaiah, specifically prophecies that were later understood to concern Christ’s death. Philip, an evangelist associated with the Twelve Apostles, asks the eunuch if he understands what he is reading. “Understandest thou what thou readest?” (Acts 8:30). The eunuch has the Bible, after all. According to Sola Scriptura, he should be fine. Right? But no — what does the eunuch say? “How can I [understand the book of Isaiah], except some man should guide me?” (Acts 8:31). In order to understand the Bible as Scripture, a third party — someone else — must interpret it for you. It is the Catholic position that this “someone else” is Tradition as understood by the teaching authority of the Catholic Church’s leaders, the Pope and the Bishops in communion with him.
It is important to remember who the Catholic faith is for, though. Faith is not for the church’s hierarchical leaders only. The Bishops defend and explain a faith that is ultimately for all people. The hierarchical leaders interpret the faith in such a way that anyone is capable of finding salvation through obedience to the teaching of Christ in the church. As Christ said to His apostles, “whoever receives you receives me” (Matthew 10:40), and “if you forgive the sins of any, they are forgiven; if you withhold forgiveness, it is withheld” (John 20:23). The Pope and the Bishops in communion with him exist for the purpose of safeguarding the faith of all Christians. All Christians are called to profess, by their life and witness, the faith of the Apostles. They are called to bear witness to the world that Christ is truly present in His mystical and visible body, the Catholic Church.
The thing is, the Bible is itself arguably a form of Tradition. It is based on the writing and testimony of the apostles and prophets. To be fair, as the priest I originally mentioned insisted during his homily, the Bible is without doubt a very privileged form of Tradition; but all the same, it is still Tradition in the sense that it originates with Tradition in the same deposit of faith that is safeguarded by the church.
The Catholic Church’s approach to the Bible is really rather reasonable. The church recognizes that neither the canon nor the interpretation of Scripture can be taken for granted, but must both be determined by persons with the authority to do so. Christ Himself foresaw the need of His people for a living authority that can speak directly to their questions — whether regarding the theology of Arius, the human and divine wills of Christ, the legitimacy of religious images, the number of sacraments, or the nature of salvation. Without a living authority — an authority that exists not only in the past in the Bible or in some council, but in an authority that exists in the present and can answer new questions and doubts that arise — Christian people fall into doctrinal crises and every kind of schism and division.
The Catholic believes it is the gift that Christ gave to Peter long ago that makes the avoidance of these sad situations a real possibility, for upon a Cephas (a “Rock”) He built His church, and the gates of hell have not prevailed against it.
“Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.” (2 Thessalonians 2:15 KJV)

“And they continued stedfastly in the apostles’ doctrine and fellowship, and in breaking of bread, and in prayers.” (Acts 2:42 KJV)