A Roman Catholic will tell you that they too believe in the authority of Scripture. They believe 2 Timothy 3:16 to be true. It’s also that they believe that when Christ gave the keys to the church, this authority meant that it would be the church or its magisterium a few hundred years later who would get to rule over what was and isn’t in Scripture. Further, alongside Scripture would tradition handed on and developed.
Here’s the problem with that:
16 All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, 17 that the man of God[b] may be complete, equipped for every good work.
That’s right. The problem is with what 2 Timothy 3:16 itself says and then what the following verse says. First, the sufficient authority of Scripture is found in who it is from and how it came to us. Scripture is sufficient and authoritative because it is God breathed, it has that quality of inspiration which guarantees its truth and accuracy. It is sufficient and authoritative because in it, God himself speaks.
Secondly, Scripture is authoritative and sufficient because of what it does. It is useful or profitable for four things: teaching, reproof, correction, training. In other words, it has both a positive role in equipping, teaching and encouraging as well as a negative role in its use to correct, challenge and discipline. God’s Word disagrees with us and when it does, we must fall into line with it.
At that point you will realise that Paul is covering all bases. Scripture provides for every type of situation we might find ourselves in, for every need that the church and the individual believer might have.
In case we still don’t get it, Paul continues in verse 17 to say that Scripture does its job, it fulfils its purpose. Scripture is useful in order to make us complete and so that we are equipped for everything God might ask of us. That’s another way of telling us that it is sufficient. Scripture gives us everything we will need as we seek to follow Christ and live for him.
For more on Scripture and Revelation see “How do you know? The Doctrine of Revelation”