First of all, we should note that Chemnitz does acknowledge the inner testimony of the Spirit that the Scriptures are the Word of God. But this does not necessarily tell us exactly what is in the canon and what's not. That is to say, one can theoretically preach the Word of God, that is, the Apostolic testimony, without having the canon of Scripture. In fact, that's what people did before the Apostles deposited the faith in the form of writings. As a result, a Christian living in the post-Apostolic era cannot hear the Word of God without hearing the content of the canon. Nevertheless, he is also faced with the historical problem with what is from the Apostles and what is not.
Therefore, early Lutheranism argued that clear historical argument could be made and had to be made about what belonged in the canon. This was fairly simple with regard to the OT. Jesus had acknowledge it as inspired and that pretty much settled it. The NT was a little more tricky. Everyone in the 16th century agreed that it was the Apostolic Tradition that was authoritative. Jesus told the Apostles that he would lead them into "all truth" by sending the Holy Spirit. Those who heard them heard Jesus. So what they said was infallible. The Roman Catholics said that this extended to the Pope, college of Bishops and unwritten tradition. The Reformers said just the written tradition, i.e. the NT. But which books go in the NT and which don't? How do we know something for sure comes form the Apostles? Didn't the Church just decide what came from the Apostles?
No, says Chemnitz in part I, the Apostles themselves established the canon!
How does this work?
Well, claimed Chemnitz, when Paul said in I Timothy that "all Scripture is God-breathed" he meant the Gospels also and the other Epistles, because they had been written before he wrote in the late 60s.
I didn't used to think this was a good argument, but I've changed my mind and think that dating the Synoptic gospels from the 50s makes sense.
How do we know Paul knew them? Because Luke used Matthew and Mark to construct his Gospel and Paul knew Luke and his writing activity.
Luke, Mark and Matthew are all self-consciously writing Scripture. Luke imitates the LXX's style. Matthew structures his writing on Torah. Mark view himself as writing a shorten form of Matthew for the unbaptized (more on how I've reached these conclusion in a future post). Paul also claimed to have the Holy Spirit in I Cor. and to have a divinely revealed gospel (Gal. 1). So, he here not only establishes the OT, but also Mark, Matthew, Luke, Acts, and his own Epistles.
Let's go beyond Chemnitz and move to Peter's witness in 2 Peter. I'm going to be basing myself on David Scaer here.
In 2 Peter, Peter attests that he saw the transfiguration in chapter 2. He quotes Matthew's Gospel and then says "we have a sure word of prophecy." Scaer argues that this is Matthew's Gospel that he is referring to, since he just quoted it. At the end of the Epistle, he notes that Paul's Epistles have already been collected into a collection and have circulated. This was probably done by Onesimus, the slave from Philemon, who later became a Bishop (this is probably the reason that letter is included!). Anyways, he says that they are hard to understand (this I think demonstrates that this is actually Peter. A author writing as Peter would not have made Peter say this) and that people distort them "like other Scriptures." In other words, Paul's letter are Scripture as well!
So, Peter establishes a canon also: Paul's Letters and Matthew. We can also count his own letters and also the Gospel of Mark, which with its Petrine inclusio is clearly authorized by him and written on the basis of his testimony.
Lastly, we turn to John. John obviously considers his own writing authoritative. As Bauckham shows, he portrays himself as the ideal witness in his own Gospel. In his Epistles he writes authoritatively and in Revelation, he claims he received the book by a Revelation of Jesus Christ, God's Angel.
Beyond this, as I noted in an earlier post, Bauckham has shown that John uses a Petrine inclusio in his Gospel and therefore acknowledges Luke and Mark (who also have one and are based on Peter's testimony) as being authoritative.
One can also note that in the early Church it was commonly thought that he named the books that were supposed to be the canon. Louis Brighton thinks that this is plausible and says that he was allowed to live so long because he would "remain" that is remain as a witness "until I come"- that is come in the form of the final canonical Scriptures. Luther also believed this.
Again, I used to think that this was not very convincing, but if you read Irenaeus in the 2nd century, basically the canon he acknowledges is the one we have. He also claims he received the Apostolic tradition from Polycarp, who received from John. It's pretty unlikely that Polycarp messed with the tradition either- so I think it's beyond a doubt in my mind that this in fact is true. John before he died really did name what books were Apostolic and belonged in the canon.
But let's just pretend that's not the case and see what we have if we go on purely written attestation form the Apostles as what's in the canon.
Paul: Synoptic Gospels, Acts, his own Epistles.
Peter: Matthew, Mark, 1 and 2 Peter, Paul's Epistles.
John: Gospel of John, Epistles of John (1,2, 3), Revelation, Luke, Mark.
Now, that pretty much covers it, except, Hebrews, James, Jude.
Interestingly enough, Lutherans have included these books in what is called the Antilougomena. The idea being that there are books that are universally attested (Gospels, Act, Paul, I John, I Peter) and then ones that have mixed attestation (Hebrews, 2 Peter, Jude, James, Revelation, 2 and 3rd John). Lutherans have taught that these books are of secondary canonicity.
In any case, Lutheran have not rejected these books because of their lack of attestation, but rather have said that one merely has to interpret them in light of the books that are better attested. Also, one cannot establish articles of the faith on the basis of these books. This is helpful in dealing with the millennium in Rev. 20 and the statement in Hebrews that makes it seem like you can't repent after baptism.
If my reasoning is correct though, this number that is consider Antilogemena clearly can be moved down to Hebrews, James and Jude.