Aelianus’s fuller exposition of his views on sola scriptura is here, and I’m going to follow his good example of putting a post-sized response in a post (since my reaction outgrew the Laodicean comment boxes almost as soon as it got started).
There seem to be two basic misconceptions about what’s even under discussion.
1) Sola scriptura is not a claim that everything which the apostles taught by word of mouth was written down. Rather it is a claim that all things necessary for faith and practice are provided by Scripture. So the fact of, eg, John saying the world couldn’t contain the books that would be needed to record what the Lord did, is no objection to sola scriptura: the claim has never been that the Bible contains all truth or everything that God has ever revealed.
2) Sola scriptura is not a claim that the Church has no authority. So prooftexts to demonstrate that the apostles had unique authority in the church, and that their successors (albeit our understanding of succession is not shared) have power to bind and loose, etc, are beside the point. The point is the nature of the Church’s authority and how it relates to the authority of Scripture: while we confess that the Church has authority to declare what Scripture teaches on doctrine and practice, the Church has no authority to go beyond Scripture in what she teaches. The Church is not meant to rely on herself to declare authoritatively on questions of doctrine or duty, but rather on Scripture.
Let me deal with one other point here before getting back to the question of sola scriptura itself: canonicity – related, but not the question itself. Questions about sola scriptura take to do with the nature of the scripture [coming back to this in the next para]; questions about canoncity take to do with what gets recognised as scripture. On the OT canon, the claim that ‘the Protestant canon of the OT did not exist in Our Lord’s time’ has no New Testament support. The Gospels record Jesus appealing constantly to a known, fixed body of writings in his disputations with the Pharisees and Sadducees, and these were the writings which the Apostles used to demonstrate the truth of their claim that the Messiah had indeed come, eg. So the strategy of discrediting the Jewish Scriptures is not only a mischaracterisation of the situation that obtained at the time of Christ but is also really fatal to the gospel of the New Testament (which relies on the revelation in the Old Testament). As for the ‘Protestant canon of the NT’ – whatever Luther’s “rejection” of any NT books looked like in practice, his views were never ‘the Protestant’ view. You don’t need to project your imagination of how a Protestant should according to your analysis view the pronouncements of a Protestant figurehead, as if Protestants just can’t help supplying themselves with inadequate Pope-substitutes who only embarrass them by saying awkward things. The Protestant canon is identified in the Protestant creeds/confessions, not the overinterpreted speculations of one Protestant theologian, and the Reformation confessions are unanimous on the extent of the canon.
Returning to: the nature of Scripture itself. Aelianus thinks I should think that most of Scripture is superfluous because I’ve said that John wrote enough to convince anyone that Jesus is the Christ. But that’s not exactly where I was going with that. The position is rather that all the Scriptures are a revelation that has been given by God himself, and as such it has certain characteristics. That means that the Gospel of John has the same qualities as any other part of God’s revelation, and vice versa. It’s not as if the Bible is a random assortment of isolated texts with no cohesion, whose message has to be treated as tentative until it gets external approbation. Rather, this is the revelation that unfolded as God gave it, and each piece that he gave both connects organically with the other pieces he gave, and has intrinsically and in its own right the properties of a divine revelation. Such as, divine truthfulness, divine authority, and divine fitness-for-purpose. The argument from John is not just that the segment in the Bible called John’s Gospel contains enough for someone to believe that Jesus is the Christ, but that John’s Gospel being a part of God’s revelation has the property of providing the basis for anyone to believe that Jesus is the Christ and have life through his name. It’s due to being what God has spoken. Not just John’s gospel but the holy scriptures in general are able to make someone wise unto salvation.
Which brings me finally round to 2 Timothy, and to say that what Aelianus gives with one hand by way of affirmation of the authority of Scripture, he takes with the other when he continues to say ‘it does not contain all that is morally necessary to persevere in God’s grace…’ Referring to 2 Timothy, Aelianus says, “That the scriptures render one complete would only constitute a claim to their sufficiency if it were the scriptures with which one began.” But there doesn’t need to be any doubt about this: as it happens, Timothy did begin with the Scriptures, as Paul’s direction makes clear: “Continue in the things which you have learned and been assured of, knowing from whom you have learned them, and that from childhood you have known the holy scriptures, which are able to make you wise for salvation.” The scriptures which Timothy had known from childhood were able – had an innate ability to accomplish their stated purpose – to make him wise for salvation. Calling Scripture ‘profitable’ doesn’t here mean that Scripture supplements something else – Paul says Scripture is profitable (for doctrine, reproof, correction, and instruction in righteousness) to make the man of God complete, and fully equipped for every good work. There’s really no wiggle room here. If the man of God wants to be perfect, or equipped for any good work, the resource he is meant to turn to is the scripture which God breathed out. Scripture claims that Scripture provides all the doctrine and instruction to make a man perfect.
The alternative is for the man to think himself wiser than Timothy, wiser than Paul who advised Timothy, and wiser than God who inspired Paul. That’s why it just isn’t good enough to affirm that Scripture is authoritative, inspired, inerrant, … and then stop short of confessing that it’s sufficient for doctrine and practice. To the extent that someone thinks that Scripture needs to be supplemented by some top-up revelation, or some parallel transmission of revelation, to that extent they are effectively rejecting the authority which Scripture itself claims for itself as the complete encapsulation of everything necessary for doctrine and practice (and then exacerbating it in proportion to the unscripturalness of the doctrines or practices which they think is included in the content of that extra revelation).