I wish to present to you an argument for Sola scriptura with 2 Thessalonians 2:15.
"So then, brothers, stand firm and hold to the traditions that you were taught by us, either by our spoken word or by our letter."
What are the traditions that St.Paul describes in this sentence? Well, one of the sources of this tradition can be found is in the letters (the Greek word can be expressed in plural) sent by the apostles. Since we have these letters, it can be referred that we have this substance of tradition that 2 Thessalonians is alluding to.
St.Peter calls these letters scriptures in 2 Peter 3:16. Thus Paul telling the Thessalonians to hold firm to the substance in the apostolic letters of the new testament, which is scripture. To additionally substantiate the claim that the traditions are identical, I suggest reading 1 Corinthians 15:3-8 (note he said preached and delivered) in context of 1 Corinthians 11:1 (notice he wrote delivered) & 1 Corinthians 11:23-26 (the reference quote is only found in Luke 22).
2 Thessalonians 2:15 request may also an incentive to form what we know as the new testament canon, all the church has to do then is find out which books were apostolic. (Papyrus 45, papyrus 46, quotes from the early church, and the Didache insinuate that's what may have happened.)
-Objection. what about the "our spoken word"? Doesn't that mean there's a separate tradition that was only passed down orally?
No, because St.Paul stated that the same tradition is found in "either the spoken word OR by our letter". (emphasis mine.) So, he must be saying these are the methodologies his audience has to use in order to obtain this tradition. (Remember, 90% of people in the first century were illiterate and they can only receive information vocally.)
Furthermore, St.Paul is not stating there's two different traditions, because he would have written "and" rather than "or" in the verse. If there was two, then the Thessalonians would've been in a position to choose one tradition over the other, which would miss the point of verse 15 if the tradition was different-or even worst, as a result, this could've caused disunity. What we know about St.Paul -from the rest of chapter within 2 Thessalonians and other letters like 1 & 2 Corinthians- is that division within Christian communities is something he critically resents. Then St.Paul is cautious enough to not allow such an opportunity for separation to spawn due to different contents.
More importantly those who erroneously say there are different teachings always emphasize that BOTH are necessary for complete understanding and are inextricable-which the verse is clearly in disagreement with if the Thessalonians have the option of either methodology to follow Paul's communiqué. So, no…two distinct traditions doesn't exist, at least according (or that we can derive from) to 2 Thessalonians 2:15.
Before I finalize everything, I would like to explain why St.Paul even mention traditions. It's important to see that St.Paul in 2 Thessalonians 2:13-15 is making a contrast from verse 2: "not to be quickly shaken in mind or alarmed, either by a spirit or a spoken word, or a letter seeming to be from us, to the effect that the day of the Lord has come." to 12 where he explains the requirements that needed before the second return of Christ (which the requirements sounds oddly like the prophecies in the gospel of Matthew). Basically, he's saying 'stop listening to rumors and follow the material we delivered to you.'
This is the overall argument:
-There is content which Paul calls tradition and he tells the church to hold firm to.
-The content can be found either by oral or written communication (but the content is the same in both cases).
-We have the written communication.
-This written communication is the writings of the apostles.
-The writings of the apostles are called scriptures.
-The tradition is part of scripture.
-Paul told the congregation to stand firm and hold to scripture.
-To stand firm and hold to scripture is fundamentally sola scriptura.
-Thus 2 Thessalonians 2:15 is affirms the biblical doctrine of sola scriptura