By Spencer D Gear
I used to understand that 2 Tim. 3:16 and the reference to “all Scripture” was referring back to the OT. Gleason Archer wrote in his consideration of 2 Tim 3:16:
‘It would never have occurred to the Greek-speaking recipients of 2 Timothy to suppose that Paul could be referring to any other writings but the inspired and authoritative books of the Hebrew canon. Nor is there the slightest suggestion in any of the recorded utterances of Jesus Christ or His apostles – or indeed in any of the writings of the New Testament authors – that there were any portions of the Hebrew Scriptures that were not authoritative and inspire’ (Archer 1982:417, emphasis in original).
In recent times I’ve been asking some further questions of 2 Tim. 3:16-17 and 2 Peter 1:20-21. The following is some tentative thinking (I have not reached a conclusion yet).
Second Tim. 3:15-17 (ESV),
“and how from childhood you have been acquainted with the sacred writings, which are able to make you wise for salvation through faith in Christ Jesus.  All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness,  that the man of God may be competent, equipped for every good work.”
Here we have two groups of writings distinguished: “the sacred writings” of v. 15 and “all Scripture” of v. 16.
“All Scripture” (v. 16) seems to indicate everything that the Holy Spirit gave to the church as canonical and authoritative, OT and NT. When Paul wrote these words, was he referring to a body of literature that was more than the OT. We know this from:
1 Tim. 5:18 (ESV), “For the Scripture says, ‘You shall not muzzle an ox when it treads out the grain,’ and, ‘The laborer deserves his wages.’”
These two sayings are clearly co-ordinated. If the first is Scripture, than so is the second. Here we have a word spoken by Jesus that is on the same level of authority as a saying from the OT canon.
1. “You shall not muzzle an ox when it treads out the grain” comes from Deut. 25:4 (You’ll find a similar use by Paul in I Cor. 9:8-12).
2. Where do we find the saying, “The laborer deserves his wages”? Its precise wording is in Luke 10:7 (ESV), “And remain in the same house, eating and drinking what they provide, for the laborer deserves his wages. Do not go from house to house.” There is a slightly different form in Matthew 10:10 (ESV), “No bag for your journey, nor two tunics nor sandals nor a staff, for the laborer deserves his food.”
It is not an impossibility that Luke’s Gospel had been completed at the time of Paul’s writing to Timothy. My ESV Bible gives the date for 2 Timothy as “the final letter written by Paul (A.D. 64-68). The ESV states that ‘Luke, a physician and colleague of Paul, probably wrote this account in the early 60s A.D.”. If that is true, then the apostle Paul could have been quoting from Luke’s Gospel. But there is another possibility that Paul was quoting from a collection of sayings or oral tradition that was in circulation and used as a source for Luke (see Luke 1:1-4).
3. So, when we combine these two quotes in I Tim. 5:18 we are beginning to see that “Scripture” may refer to both OT and NT. So “all Scripture” (2 Tim. 3:16) also could refer to all that is breathed out by God — OT and NT.
We should not find this surprising, based on John 14:26 (ESV), “But the Helper, the Holy Spirit, whom the Father will send in my name, he will teach you all things and bring to your remembrance all that I have said to you.”
There’s further information in 2 Peter 3:15-16 (ESV),
“And count the patience of our Lord as salvation, just as our beloved brother Paul also wrote to you according to the wisdom given him,  as he does in all his letters when he speaks in them of these matters. There are some things in them that are hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other Scriptures.”
Peter, the apostle, confirms that Paul’s writings are of the SAME class as “the other Scriptures” (OT and NT).
I have not come to firm conclusions, but the above considerations do cause me to think again on the meaning of “all Scripture” in 2 Tim. 3:16.
These are just some thoughts from a fellow traveller.
Archer, Gleason L 1982. Encyclopedia of Bible Difficulties. Grand Rapids, Michigan: Regency Reference Library (Zondervan Publishing House).
Copyright © 2012 Spencer D. Gear. This document last updated at Date: 16 October 2015.