One can easily make the case that a New Testament, or a canon of the new covenant Scriptures, was expected. When we examine the Mosaic covenant, we notice in Hebrews 9:18–21 the facets making up the first covenant that appears in Exodus 24:3–8, and among them is the book (Heb. 9:19). Unlike the first covenant, no tabernacle or vessels in the New Covenant are cleansed because the church and individual Christians are God’s temple (1 Cor. 3:16; 6:19). Nevertheless, we who comprise the church and are of the Way are sprinkled with the lamb’s blood in our baptisms, and in due course, a book would necessarily emerge. Now, this perspective isn’t accepted by everyone. Some scholars contend that the New Testament could not have been foreseen and wasn’t expected. Others contend that the canon wasn’t created until the end of the second century CE, but I tend to disagree with both of those propositions.
The earliest hint of an emerging canon appears in 2 Peter 3:16. Peter recognizes Paul’s writings as on par with Scripture. What he has in mind when referring to Paul’s letters isn’t altogether clear, because Paul wrote some letters that were widely accepted while others were questionable. Peter assumes that his audience knows what he’s talking about, and he likely expects that they receive his own letter similarly given that he addressed himself as an apostle (2 Peter 1:1; cf. 2 Peter 3:2). Another hint at recognizing authoritative writings in the first century is 1 Timothy 5:18, which is a quotation from Luke 10:7 and Deut. 25:4. The opening phrase, “For the Scripture says,” recognizes both passages as being Scripture. This initial phrase comes from Deut while the rest is identical to Luke’s wording. Thus far, Paul’s writings and Luke’s gospel account are considered Scripture on the basis of internal evidence from the letters.
Another aspect worthy of considering is the nature of public readings in the assembly. In several New Testament letters, we observe the command to have them read publicly which indicates that they carried authority (Col. 4:16; 1 Thess. 5:27; 2 Cor. 10:9; Rev. 1:3). We’re able to base this conclusion, in part, on how portions of the Old Testament were read in synagogue meetings (Luke 4:17–20; Acts 13:15; 15:21). Other scholars have additionally pointed out that the Greek structure of Matthew and Mark lent itself to a liturgical structure—which means that they would have been used for year-round public readings. The fact that such letters were urged to be read publicly along with Paul’s command to “devote yourself to the public reading of Scripture” (1 Tim. 4:13) may in fact suggest that he already believed his writings to have been such (cf. 2 Peter 3:2).
The earliest historical source about a Christian assembly details the authority of the apostolic writings.
And on the day called Sunday, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things.Justin Martyr, 1 Apol. 67.3
What’s clear from history is that Scripture were not exclusively read in early church assemblies. Some popular writings that were often read in the church, but that were not placed among the acknowledged books, was The Shepherd of Hermas (Eus., Eccl. Hist. 3.3.6; cf. Rom. 16:14) and 1 Clement (Eus., Eccl. Hist. 4.23.11). Serapion, the Antiochian bishop (190–211 CE) wrote to dispel the Gospel of Peter that had been read in Rhossus because it had led some astray (Eus., Eccl. Hist. 6.12.2). Certain epistles were well esteemed because of the author, while others were forgeries.
Some might find the notion of reading non-canonical letters in the assembly challenging. However, the reason these writings weren’t ultimately included in the canon was because they were not universally accepted. There were three criteria for canonicity: 1) universality, 2) apostolicity, and 3) orthodoxy. If a writing fit into all three, it was accepted into the canon. However, there’s debate over another point: did the church create the canon? If so, authority primarily rests with the church—which is what Catholics and Orthodox believe, their definition of “church” here meaning the priesthood. However, while it’s true that prelates assembled to formalize the canon, they didn’t “determine” so much as “acknowledge” what had, up to that time, been regarded as Scripture. From the latter point of view, Scripture is more authoritative. This is the great divide between Protestants and Catholics/Orthodox.