In the second century, the Muratorian Canon condemned both the letter to the Laodiceans and the letter to the Alexandrians because both were “forged in Paul's name."21 One of the proofs of forgery was a lack of early attestation. In fact, if a work was found to be of recent origin, even if its authorship was not in doubt, it was not considered to be canonical. For example, the Muratorian Canon rejected the Shepherd of Hermas because, though it was edifying literature, it was composed “very recently, in our times, in the city of Rome." Lack of antiquity was the sole reason for its rejection, for this document was written after the time of the apostles.22
Eusebius echoes this sentiment. In the first quarter of the fourth century, he spoke about the New Testament canon at length....at least twenty of the twenty-seven New Testament books were already accepted by his time and that the rest were tentatively accepted. It is worthwhile to see all of his reasoning and why some books were to be rejected outright:
At this point it seems reasonable to summarize the writings of the New Testament which have been quoted. In the first place should be put the holy tetrad of the Gospels. To them follows the writing of the Acts of the Apostles. After this should be reckoned the Epistles of Paul. Following them the Epistle of John called the first, and in the same way should be recognized the Epistle of Peter. In addition to these should be put, if it seem desirable, the Revelation of John, the arguments concerning which we will expound at the proper time. These belong to the Recognized Books (homolegoumena). Of the Disputed Books (antilegomena which are nevertheless known to most are the Epistle called of James, that of Jude, the second Epistle of Peter, and the so-called second and third Epistles of John which may be the work of the evangelist or of some other with the same name. Among the books which are not genuine must be reckoned the Acts of Paul, the work entitled the Shepherd, the Apocalypse of Peter, and in addition to them the letter called Barnabas and the so-called Teachings of the Apostles. And in addition, as I said, the Revelation of John, if this view prevail. For, as I said, some reject it, but others count it among the Recognized Books. Some have also counted the Gospel according to the Hebrews in which those of the Hebrews who have accepted Christ take a special pleasure. These would all belong to the disputed books, but we have nevertheless been obliged to make a list of them, distinguishing between those writings which, according to the tradition of the Church, are true, genuine, and recognized, and those which differ from them in that they are not canonical but disputed, yet nevertheless are known to most of the writers of the Church, in order that we might know them and the writings which are put forward by heretics under the name of the apostles containing gospels such as those of Peter, and Thomas, and Matthias, and some others besides, or Acts such as those of Andrew and John and the other apostles. To none of these has any who belonged to the succession of the orthodox ever thought it right to refer in his writings. Moreover, the type of phraseology differs from apostolic style, and the opinion and tendency of their contents is widely dissonant from true orthodoxy and clearly shows that they are the forgeries of heretics. They ought, therefore, to be reckoned not even among spurious books but shunned as altogether wicked and impious.23
Beyond the twenty or more books Eusebius considered undisputed, some books were disputed because of doubts about authorship or antiquity. But if they were sufficiently early and widely read, they were considered as possible candidates for the canon. Finally, other books were rejected outright because they were of recent vintage or plainly taught error. Thus, forty years before the first definitive canon list of twenty-seven books was composed by Athanasius in 367, the church already had been wrestling seriously with the criteria of canonicity: apostolicity, catholicity, and orthodoxy. The heretical books failed all three tests.
Second, the heretical gospels were products of the second and later centuries....One piece of evidence that supports this is found in the very first canon list, produced by the heretic Marcion in about 140. Marcion lists only Luke and ten of Paul's letters in his canon. As noted previously, Marcion was a Docetist, whose views would be largely compatible with Gnostic teaching. Why then did he include parts of only our New Testament in his list? Why didn't he include such Gnostic works as the Gospel of Thomas or the Gospel of Mary or the Acts of Peter? The most likely inference is that these books did not yet exist, or they were too new to be regarded as authentic.
J. Ed Komoszewski, M. James Sawyer, Daniel B. Wallace, Reinventing Jesus: What the Da Vinci Code and Other Novel Speculations Don't Tell You, p. 145-148