Within thirty to thirty-five years of the apostle John’s death, there is ample evidence that all four of the gospel accounts and the letters of Paul were known and in use. Clement, Polycarp, and Ignatius all referenced the majority of the New Testament material casually and accepted it as authoritative without argument. Only Mark, 2 and 3 John, 2 Peter and Jude are not clearly attested. Even more important than this is the fact that Clement, Barnabas, and Ignatius all clearly make distinctions between their own words and the inspired, authoritative apostolic writings. This continued into the second half of the second century with Irenaeus who argued for the use of four gospels. Irenaeus also referenced Acts, 1 Peter, 1 John, Revelation, and all of the Pauline epistles except Philemon in his writings.
Around A. D. 140, Marcion (ca. 85 – 160), whose father was bishop of Sinope in Pontus, compiled a list of books he considered to be true Christian Scriptures. Marcion, for whatever reason, had an enigmatic dislike of both Judaism and the material world. The latter is likely a result of the influence of Gnosticism though Marcion differed with Gnostics by rejecting allegory and speculation. In creating his own canon, Marcion rejected the entire Old Testament. The version of the New Testament issued by Marcion consisted of a version of Luke’s gospel edited to exclude all references to Judaism and ten Pauline epistles that specifically excluded the pastorals. This exclusion, however, was unlikely to have been intentional. Collections of Paul’s epistles were circulating by this and Marcion likely had a collection much like the Chester Beatty codex he worked from. Like the Chester Beatty codex, Marcion’s likely did not contain the Pastoral Epistles.
Marcion was branded a heretic and he was stripped of fellowship with the church in A. D. 144. Afterwards, Marcion founded his own church that survived for several centuries. Though Marcion was defeated, the need for an official listing of authoritative writings became clear. The church at large began to compile a list though it should be noted that this was not a formal movement of the church but rather a gradual forming of a consensus over a period of time. As noted earlier, the four gospels were accepted very early as well as Acts and the Pauline epistles.
The early adoption of four gospels was important in the second century as the church fought against the spread of Gnosticism and Marcionism. With four gospels, there was a consensus concerning the basic issues which were much more effective and convincing than claiming possession of a secret gospel by heretical groups. The church made the claim that it held the true teachings of Jesus. The church also accepted the Old Testament as did Jesus and His apostles, including Paul.
The importance of apostolic succession is made an issue. If Jesus has secret knowledge to pass on, He would have done so through his apostles who in turn would have also passed it down to their disciples. Since no secret knowledge had been passed down, the church declared none existed. Later in the development of the church the idea of apostolic succession would take on additional meaning. At this time, it was enough to simply defeat the heresy being taught by those whose understanding of Jesus’ teaching differed from the church.
The defeat of the Gnostics and Marcionites did not stop others from writing their own gospels. Tatian (c. 120 – 180), a pupil of Justin Martyr wrote a harmony of the four gospels called the Diatessaron. While not a canonical book, it did attest to the equal status that the four gospels enjoyed by this time. The Diatessaron took root in Syriac-speaking churches and was the preferred text for the next two centuries. The people who had come to use the Diatessaron were very reluctant to give it up but finally did so in fifth century under episcopal pressure.
Also dating to about A.D. 170 is the Muratorian Canon which listed all of the New Testament books with the exception of 2 Peter and excluding all other writing. It is possible that the reference to the Apocalypse of Peter may be the book of 2 Peter. If this is indeed the case then the Muratorian Canon would be the oldest list of the New Testament canon. As the second century draws to a close, the writings that were to become the New Testament are generally accepted by the church though not necessarily in their entirety in all places. Eventually, the universal acceptance of the 27 books of the New Testament would be achieved.
 Comfort, 73. The Muratorian Canon state that is accepts the Apocalypse of John and Peter. In his book The Canon of Scripture, Bruce dates this canon closer to the end of the second century. This is interesting in that Bruce also contributed to the book which Comfort served as both a contributor and editor.