|St John's Vision on Patmos|
So the question is when did Sola Scriptura begin? When did it become God's will for every Christian to look to the scriptures as the final authority in matters of faith and morals? One answer many protestants give is at the death of the last apostle. At that point all the books of the New Testament had at least been written. The cannon was far from being settled but that is another can of worms. If they could figure out the cannon they could proceed with Sola Scriptura and that is what God would want them to do.
You see what happens here. The death of the last apostle becomes a huge even in salvation history. The whole life of the church needs to change on the day St John the Apostle enters his heavenly glory. What day was that? Christians didn't bother recording it. Why not? Up to that point they were allowed to use oral tradition. St Polycarp would listen for hours to St John tell stories about Jesus. It would not matter if those stories were recorded in scripture or not. John was there. What more do you need? St John tells us in his gospel that there were many stories he did not include (Jn 20:30, Jn 21:25).
As long as Sola Scriptura was not in place these stories would have huge authority in defining the faith. Remember they are devoted to the teaching of the apostles. But once Sola Scriptura kicks in these stories have no authority at all. All that matters is what does scripture say. That is a pretty big change. How did they figure it out? How did they communicate it? There is no evidence they did either.
It gets worse. There was a controversy in Corinth near the end of the first century. St Clement is Bishop of Rome. They take the issue to him. Is this before or after the death of the last apostle? We don't know. Nobody involved with the controversy bothers to note whether St John is still alive in Ephesus or not. If the way the church resolves questions changed with the death of the last apostle would that not be important?
The historical reality is nothing changed with the death of the last apostle. They had ordained successors which were called bishops. They put them in charge of the church in every town (Titus 1:5). Read the letters of St Ignatius of Antioch. He can name who is in charge of the church in every city he writes to. Only the apostles had the ability to put those bishops in place. Christians were devoted to the teaching of the bishops just as much as they were to the teaching of the apostles. Sola Scriptura simply didn't happen. It was not on anybody's radar. It is important because once you establish that the first succession from the apostles was valid then you need a really strong reason not to believe they are all valid.