Question: Where in the Bible is Sola Scriptura taught? 2 Timothy 3:15-17 is a reference to the Old Testament and does not deal with which books are inspired and how we know which books are inspired. As a former Protestant myself I wrestled with this question and frankly no one ever gave me a satisfactory answer.

Answer: The doctrine of Sola Scriptura, like the doctrine of the Trinity, is not based on a single proof text. The passage you mentioned is one of the many scriptures that support the sufficiency of the Bible as the only infallible rule of the Christian faith.

Let's take a look at this verse.The apostle Paul writes to Timothy:

“And that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus. All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work” (2 Timothy 3:15-17).

From this passage we can deduce, firstly, that the Scriptures give us the knowledge necessary to experience salvation – they are “able to make you wise for salvation through faith which is in Christ Jesus.” Secondly, the Bible is also useful for doctrine and guidance in the Christian life. Whoever is led by the Scriptures is described as “complete, thoroughly equipped for every good work.” The Bible is therefore enough to show God's children how to be saved and to live for His glory.

I agree that the primary reference to "scriptures" in this context is the Old Testament because the writing of the New Testament was not yet complete, the canon of the NT was not yet fully known, and the Scripture that Timothy was taught in his infancy was the Old Testament.

But is it possible that Timothy was aware that other inspired books were being added? And that "from infancy" to the time he received Paul’s letter, Timothy came to know of other inspired writings in addition to the Old Testament books? For instance, 2 Peter 3:16 classifies Paul’s epistles with "other scriptures" – implying that the Pauline letters were already being considered in the apostolic churches as divinely inspired and on the same level as the books of the Old Testament.

In his first letter to Timothy, Paul quotes from the Old Testament (Deuteronomy 25:4) and from a New Testament book (Luke 10:7). ‘For the Scripture says, "You shall not muzzle an ox while it treads out the grain," and, "The laborer is worthy of his wages"’ (1 Timothy 5:18). It is highly significant that Paul refers to the Gospel of Luke as Scripture on par with the Old Testament. Thus Timothy was fully conscious that the Holy Spirit was adding inspired books to the Holy Scriptures. It is therefore preposterous to limit Paul’s statement in Second Timothy on the value of the Scripture to the Old Testament.

Paul’s statement about the perfections of the Old Testament Scriptures (holy, inspired) is applicable to all Holy Scriptures in general. It's like saying, “All dogs bark.” Barking is not only the characteristic of the dogs that are now living, is it? The dogs that would be born in the future will do the same…because they are dogs. Similarly, what Paul said about the Old Testament books would certainly apply to the New, because like them, they have the same Divine author.

Still, you may say, Paul was referring to the Old Testament and not the completed Bible. This is what I call a felicitous problem! For if the Old Testament books were enough to make us wise unto salvation and equip us for every good work, how much more the whole Bible? If the Old were enough, the whole is overflowing with plenty! Yes, the Bible is able to make you wise for salvation, which is by faith in Christ Jesus. Don’t let anyone take away this blessed truth by claiming that you need some additional source to give you some vital information that is absent from Scripture.

Further, you correctly observe that this passage “does not deal with which books are inspired and how we know which books are inspired.” It’s true, it does not. However I want you to notice an interesting fact. Timothy, his mother, and his grandmother somehow knew which books were inspired, even though there was no infallible magisterium to tell them. Paul did not need to spell out the table of contents because evidently Timothy knew what these books were.

The Holy Scriptures are the property and the inheritance of the people of God and they pass them on from one generation to another. How did you first learn that the book called the “Holy Bible” is the Word of God? Was it not from your parents or from your Sunday School teacher or your pastor or some other Christian? Even though they are not infallible, the Lord used them to place in your hands His book and the doctrines therein.

If you insist on the need of an infallible authority to assure you which books are inspired, well, in that case you should not stop there either. You should then ask, “How do I know for sure that the church magisterium is infallible?” You can’t say, “Because the Bible says so” (since as a Catholic, you cannot be sure that the Bible is inspired apart from the teaching of the infallible church); and you can’t say either, “Because the church says so” (because that is begging the question).

You may wonder how people like Timothy, you and I, could know which books are inspired apart from an infallible church. Could we not trust in God who inspired the Bible in the first place? He gave the Scriptures to His people, and He could use them (weak and fallible as they are) to recognize His Word, and pass it on to future generations. I am convinced that this is exactly what God did.