That exchange made me wonder: how would explain the argument for biblical authority, to a secular person, as quickly and logically as possible? Obviously I wouldn’t assume someone could be persuaded by a few hundred words - and in my experience, people who fire expletives around on Twitter are not usually looking to be persuaded of anything anyway - but I thought it might be helpful to lay out the argument, at least as I see it, both to give an example of how a Christian might respond, and to help a sceptic identify the point in the argument at which they differ. (Usually, it comes down to the resurrection. If I believe Jesus is alive, I probably accept biblical authority, even if I nuance it differently from other Christians; if I don’t, then I don’t. On the basis of 1 Corinthians 15:12-19, I think Paul would be with me on that).

So here’s my argument for biblical authority in twelve steps.

1. There are multiple, literarily independent, first century historical sources that attest to the empty tomb and/or the resurrection appearances of Jesus of Nazareth. (For the very sceptical, this can be established by learning Koine Greek and visiting the Chester Beatty Library, the British Museum, and so on).
2. Historical scholars generally agree that this is because the tomb of Jesus was empty, and his followers had experiences which they understood to be resurrection appearances. (See, for summaries of and engagement with recent scholarship, N T Wright, The Resurrection of the Son of God; Geza Vermes, The Resurrection; Michael Licona, The Resurrection of Jesus: A New Historiographical Approach; and so on).
3. If miracles are possible, the most likely explanation of this evidence is that Jesus of Nazareth was bodily raised from the dead. If miracles are impossible, an alternative explanation - hallucination, conspiracy, swoon, other - is required. (This is argued compellingly in the books cited above, and implicitly conceded in the work of many sceptical writers on the resurrection, including well-known non-Christians like Vermes, Bart Ehrman and others).
4. If the existence of a creator God is possible, then miracles - understood as suspensions of natural laws as a result of divine action - are possible, since a creator God could act in any way they chose. (The first half of my If God, Then What? lays this out in a bit more detail; for a lot more detail, see Craig Keener’s Miracles).
5. The existence of God is possible. (Philosophically, this may be the most contentious premise so far - but since anyone denying it has to show the impossibility of God, and that has proved beyond the reach of most, I consider it fair game).
6. Therefore miracles are possible (from #4, #5).
7. Therefore the most likely explanation for the historical evidence we have is that Jesus of Nazareth was bodily raised from the dead (from #3, #6).
8. If Jesus of Nazareth was bodily raised from the dead, the most likely meaning of this event is that Israel’s God has vindicated and exalted him as Lord. (Almost all interpreters in history who accept the resurrection have agreed with this conclusion; a fascinating exception is the Jewish scholar Pinchas Lapide, who believes it means that Jesus was a great prophet to whom Israel should have listened).
9. If Israel’s God has vindicated and exalted Jesus as Lord, then we should accept and embrace his view of the way God’s authority functions in the world. (Again, almost everyone in history who believe Jesus was resurrected has believed something like this).
10. The historical evidence we have indicates that Jesus of Nazareth believed divine authority was expressed through (a) the Hebrew scriptures, (b) his own prophetic teaching and actions, and (c) the teaching and actions of those whom he delegated as apostles. (This involves seeing the canonical gospels as broadly reliable records of Jesus’ ministry based on eyewitness testimony; see e.g. Richard Bauckham, Jesus and the Eyewitnesses; N T Wright, Jesus and the Victory of God; and so on).
11. The Bible is the collection of (a) the Hebrew scriptures (Genesis to Malachi), (b) Jesus’ own prophetic teaching and actions (Matthew to John), and (c) the teaching and actions of those whom he delegated as apostles (Acts to Revelation). (It is of course open to anyone to object that, properly speaking, several of these books were not written by apostles. Rather than entering into a protracted defence of the Protestant canon here, I will simply direct the reader to Michael Kruger’s Canon Revisited, and point out that even if someone disagrees with him, they would still need to concede the authority of the vast majority of the Bible).
12. Therefore we should accept and embrace the authority of the Bible (from #8, #9, #10, #11).

As I often find myself saying, that is not an objective “proof” for the authority of scripture. That would be like proposing an objective “proof” for trusting empirical sense data, or the efficacy of human reason. But it might well serve as an effective way of identifying where the disagreement in these conversations really lies. Like so many things, it comes down to our answer to the question, “Who do you say that I am?”