macarthur breaks this down well...
no oneeven the most impassioned champion of sola Scripturawould deny that Paul had taught the Thessalonians many things by word of mouth. No one would deny that the teaching of an apostle carried absolute authority. The point of debate between Catholics and Protestants is whether that teaching was infallibly preserved by word of mouth.
So the mere reference to truth received firsthand from Paul himself is again, irrelevant as support for the Catholic position.
Nothing here suggests that the tradition Paul delivered to the Thessalonians is infallibly preserved for us anywhere except in Scripture itself.
In fact, the real thrust of what Paul is writing here is antithetical to the spirit of Roman Catholic tradition. Paul is not encouraging the Thessalonians to receive some tradition that had been delivered to them via second- or third-hand reports.
On the contrary, he was ordering them to receive as infallible truth only what they had heard directly from his own lips.
Paul was very concerned to correct the Thessalonians' tendency to be led astray by false epistles and spurious tradition. From the very beginning the Thessalonians had not responded to the gospel message as nobly as the Bereans, who "received the word with great eagerness, examining the Scriptures daily, to see whether these things were so" (Acts 17:11).
It is highly significant that the Bereans are explicitly commended for examining the apostolic message in light of Scripture. They had the priority right: Scripture is the supreme rule of faith, by which everything else is to be tested. Unsure of whether they could trust the apostolic messagewhich, by the way, was as inspired and infallible and true as Scripture itselfthe Bereans erased all their doubt by double-checking the message against Scripture. Yet Roman Catholics are forbidden by their Church to take such an approach! They are told that the Church through her bishops dispenses the only true and infallible understanding of Scripture. Therefore it is pointless to test the Catholic Church's message by Scripture; for if there appears to be a conflictand make no mistake, there are manyRome says her traditions carry more weight that her critics' interpretation of Scripture.
What the apostle was telling the Thessalonians was nothing like what Rome tells faithful Catholics. Paul was urging the Thessalonians to test all truth-claims by Scripture, and by the words they had heard personally from his own lips. And since the only words of the apostles that are infallibly preserved for us are found in Scripture, that means that we, like the Bereans, must compare everything with Scripture to see whether it is so.
Roman Catholic apologists protest that only a fraction of Paul's messages to the Thessalonians are preserved in the two brief epistles Paul wrote to that church. True, but may not we assume that what he taught the Thessalonians were the very truths that are found in generous measure throughout all his epistlesjustification by faith, the true gospel of grace, the sovereignty of God, the Lordship of Christ, and a host of other truths? The New Testament gives us a full-orbed Christian theology. Who can prove that anything essential is omitted? On the contrary, we are assured that Scripture is sufficient for salvation and spiritual life (2 Tim 3:15-17). Where does Scripture ever suggest that there are unwritten truths that are necessary for our spiritual well-being? One thing is certain: these words in 2 Thessalonians 2:15 imply no such thing.
