Among those who study the NT canon, many believe the NT writings were not considered Scripture (on par with the OT) until around AD 200. Michael Kruger has addressed this issue in the fifth chapter of his book, The Question of Canon, which I have summarized for Books At a Glance. They have a great monthly and annual subscription to their entire database of summaries, with one or two new summaries each week, covering theological and pastoral books. You can sign up for a 30-day trial to check it out; I think it’s definitely worth the money.

Below is the part of my summary covering chapter 5 of Kruger’s Question of Canon, and I agree with his approach so I wanted to share the treatment of the evidence.

Many modern scholars have settled on c. AD 200 as the earliest period at which the New Testament writings were considered Scripture. Irenaeus has been called the “principal architect” of the canon, while another scholar has said Irenaeus “essentially created the core of the New Testament canon of Holy Scripture.” But a fresh examination of the evidence suggests that the New Testament writings were considered Scripture far earlier than Irenaeus.

We will start with Irenaeus and move backward. Irenaeus does not use Scripture in a way that suggests he is doing something new. He cites it throughout Against Heresies, until Book 3, in an assuming and unapologetic manner. He also recognizes the fourfold Gospel and that it had to be fourfold because of the four corners of the earth. While some scholars believe Irenaeus is here trying to substantiate the Gospels as Scripture, it is more likely he is “simply offering a retrospective theological explanation for a longstanding church tradition” (161).

Then there are contemporaries of Irenaeus. The Muratorian Fragment recognizes twenty-two books as Scriptural. It traditionally dates to c. AD 180, but some scholars recently have tried to push it forward to the fourth century. None of these new arguments are convincing, though, so we have a canonical list as early as AD 180. Theophilus of Antioch write To Autolycus around AD 177, in which he argued that Christian writings had the same level of integrity and authority as Old Testament writings because of their common inspiration by the Holy Spirit (Autol. 3.12). In this letter he cites Matthew, John, and Luke, and elsewhere created a Gospel harmony of all four Gospels (Jerome, Epist. 121.6.15). Tatian’s wrote his harmony, the Diatesseron, in the same period. Clement of Alexandria employed New Testament passages throughout his writings, even claiming our four Gospels are the only true ones. He cites Matthew 757 times, Luke 402 times, John 331 times, and Mark 182 times.

Prior to Irenaeus, we have Justin Martyr, who mentored Tatian, suggesting Justin also knew of the four Gospels. Justin refers to “gospels” (1 Apol. 66.3) that were written by the apostles (Dial. 103). He also cited from all three Synoptic Gospels, and seems to have borrowed his logos terminology and some themes from John’s Gospel. Although some have questioned whether he viewed them as Scripture because he calls them “memoirs of the apostles,” he is probably using Papias’s language, and he speaks of them as on par with the Old Testament prophets (1 Apol. 67.3).

The apostolic fathers are difficult to handle in this regard, but they show much evidence that they regarded the apostles’ writings as authoritative Scripture. When they use language reminiscent of New Testament passages, sometimes even verbatim, some scholars claim we cannot know for sure that they were citing written texts. But this supposition is problematic. It assumes Christians were averse to written texts and preferred oral tradition into the second century, which we have seen is erroneous. The apostolic fathers were also quite literate, suggesting they would have been very interested in written texts. Even the Gospels writers themselves rely on written sources (e.g., Luke 1:1–4). Also, certainty is too high a bar for historical investigation. It is more plausible to believe the apostolic fathers were citing apostolic writings when the wording is verbatim or nearly so, than to believe they were recording hypothetical oral tradition or hypothetical written sources.

Papias, around AD 125, supposedly learned about the Gospels from John the Elder (Eusebius, Hist. eccl. 3.39.3–4, 15–16). Papias is clear that the Gospels originated from the apostles, or through their testimony. Papias also knew 1 John, 1 Peter, Revelation, and some Pauline epistles, and likely knew John’s Gospel.

The Epistle of Barnabas (c. AD 130) cites Matt 22:14 nearly verbatim and introduces the citation with “it is written,” suggesting the author is citing the written Gospel. Ignatius knew at least some of Paul’s letters and even mentioned them in Eph. 12:2. Ignatius also clearly understood the apostles to be as authoritative as Christ and refers to their writings as having “decrees” and “ordinances,” words use of Old Testament law. Polycarp knew John personally and mentions Paul several times in his letter to the Philippians as having far more authority than him as a bishop. He also tells his readers to read Paul’s letters (Phil. 3.2). First Clement (c. AD 96) relied heavily on Paul’s letters and regarded the apostles as having the authority of Christ himself (1 Clem. 42:1–2).

Finally, in the New Testament, 2 Peter 3:16 refers to Paul’s letters as on par with the Old Testament. First Timothy 5:18 also cites a combined quotation of Deut 25:4 and Jesus’ saying in Luke 10:7, referring to them both as Scripture.
In sum, Irenaeus did not first recognize the apostolic writings as Scripture. His contemporaries and those before him, even Peter and Paul themselves, recognized that the apostolic writings carried the same authority as Christ’s words.

Preview or buy Kruger’s Question of Canon here. You won’t be sorry!