To answer the question appropriately, it is necessary to emphasize three points: (1) Jesus’ commissioning of the disciples and the importance of Pentecost in identifying the powers and responsibilities of the new Christian Church; (2) the use of specific texts in early Eucharistic liturgies, and (3) the role of Sacred Scripture in protecting the tradition of the teachings of the Lord Jesus necessary for salvation.
We know that in several Gospels Jesus commanded his disciples to teach everything he had taught them. For at least one generation the essentials of Jesus’ teachings were passed down orally; St. Paul is the first to use the written word, in his famous Epistles which date to around 51 A.D. and the following decade. Interestingly—and this is important down the road—Paul wrote about the meaning of Jesus and virtually nothing about his biography. However, as the first witnesses died off, and the Church—under the inspiration of the Spirit—came to a deeper sense of the meaning of Jesus in the plan of history—a Christian named Mark put to paper a “theological biography” for Christians in his region of Rome undergoing persecution. Other authors began to imitate Mark—among them Matthew, Luke and John.
When these texts began widespread circulation throughout the Roman world, we see their importance in the primitive form of the common Eucharist. We have a remarkable surviving description of a Christian Eucharist in c. 150 A.D. from St. Justin Martyr, the great apologist who was defending Christianity against the charge of cannibalism. Regarding what we would call today the “Liturgy of the Word,” Justin states that when the assembly was gathered, “The recollections of the Apostles or the writings of the (Hebrew) prophets are read, as long as there is time.” After this, “the president of the assembly speaks to us; he urges everyone to imitate the examples of virtue we have heard in the readings. “ A more complete description is found in the Office of Readings for the Third Sunday of Easter.
As you might expect, a natural winnowing process continued in church worship, as certain texts and authors were used more frequently by bishops, presiders, and the faithful at large, texts believed the best embody the core of God’s revelation through Jesus. Christians, of course, revered the Hebrew Scripture and integrated them into the early Eucharist. Thus what would eventually be called “The New Testament” began to take shape as the product of the Spirit’s revelation given both to the authors and the community that received their texts.
The need to establish formal recognition of which books were precisely considered canonical, that is, belonging to the canon or collection of God’s revelation, became evident around 200 A.D. with the teaching of Marcion of Sinope. One of the early Church’s truly interesting rogues, Marcion denied the God of the Hebrew Scripture and produced a bowdlerized edition of St. Luke’s Gospel. This was the last straw, and Church bishops and theologians coalesced around the 27 books we know today as the New Testament, a very new term in 200. By the year 400 A.D. we can see in writings of Church Fathers a general acceptance of these books as inspired, containing everything necessary for the attainment of salvation.
Were there books that “missed the cut,” so to speak? Absolutely. A few that come immediately to mind are Gospels attributed to St. Peter and St. Thomas, which you can purchase on Amazon. They were passed over because of questions of authorship, but more likely because of content. The Church showed an amazing collective wisdom in selecting works essential to the core of Jesus’ message of salvation. The “also-ran” books are popular today in part because they often purport to give us lost information about Jesus. Again, the books of the New Testament Canon are focused on the meaning of God’s plan and Jesus’ words and acts. If biographical detail had been critical, St. Paul would have never made the cut.
Over time the Church has taught that the Age of Revelation concluded with the death of John the Apostle, traditionally believed to be the last living author of the New Testament. This is why the Church in general (and me, to be honest) tends to downplay visions and apparitions even in the present day, on the grounds that even Marian apparitions cannot add new information to the New Testament canon. The Church permits private and even occasionally public popular devotion to saints and their divine appearances when they reinforce the established truth of the Canon, as in the case of St. Margaret Mary and devotion to the Sacred Heart.
For many complicated reasons, classical Protestantism differs from Roman Catholicism on the exact books of the New Testament Canon. So, that bible you stole from the Days Inn motel room years ago may not have the Epistle of James, for example, which ironically reminds us that faith without good works is worth nothing…so stop stealing motel room towels, too.