Jesus came back to the Temple; and as he taught, the chief priests and the elders came to the servant of the word and asked, "What authority do you have to say these things? Who gave you this authority?"
Jesus answered them, "I will ask you just one question, and if you give me an answer, I will tell you what authority I have to do these things. Where did John's authority to baptise come from: was it from God or from human beings?"
They started to argue among themselves, "What shall we say? If we answer, 'From God,' he will say to us, 'Why, then, did you not believe John?' But if we say, 'From human beings,' we are afraid of what the people might do, because they are all convinced that John was a prophet."
So they answered Jesus, "We don't know."
And he said to them, "Neither will I tell you, then, by what authority I do these things." (Matthew 21:23-27)
I suggest this parable is instructive for considering the authority of Scripture.
Where does Jesus Christ's authority come from? In terms of this dialogue, Jesus implies that his authority is similar to John's. It comes from God and it is recognised by the people. (The people cannot and do not bestow authority on John the Baptist, but they can perceive the authority of God working in him, recognise it, and, by submitting to baptism, receive that authority).
The religious leaders who question him are confronted with a question which challenges their pose as questioners. Why do they not recognise the divine authority of John the Baptist or of Jesus? Why do they not understand, acknowledge and join with the reception of that authority given by the ordinary people?
Within this exposition of the authority of Jesus Christ, via a subtle question-and-question dialogue, we see important elements concerning divine authority. Such authority is not bestowed by the non-divine (i.e. humanity). No committee or council of the wise and powerful determines that Jesus has divine authority. There is no election of Jesus to the position of Son of God via democratic vote. Yet such authority is meaningless among humanity if it is not recognised and received by humanity. In human terms the authority of Jesus is 'self-authenticating.'
The subtleties of Jesus' divine origin and divine power, of recognition and non-recognition, of reception and rejection are well worked out in John's Gospel, notably in chapter 8, particularly in verses 14-19 and 54-58.
What then of the authority of Scripture in the life of the church?
I suggest the claim, at least in evangelical theological expression, has similarities with the authority of Christ himself, as expounded above and in John 8.
First, the authority of Scripture as the writing down of the divine Word or message of God both comes from God and is (and was) recognised by the people. The decision regarding what was in the canon of Scripture and what was not was a decision about recognition and reception by the people of the church of which circulating scriptures were of divine origin and authority and which were not. The church did not write Scripture in such a mode that it could later rewrite it. Nor did the church determine the canon of Scripture in such a way that a later vote could determine it to be otherwise. What was determined was what had been universally received by the whole church as God's Word written down and what had not.
Secondly, the authority of Scripture as similar to the authority of Christ is less than the full story. In an important sense the authority of Scripture is the authority of Christ. For the Christian Scripture, of Old Testament and New Testament, is the message of Christ. The Old Testament informs that message and provides the context for its reception. The New Testament is the gospel of Christ (according to four authors/authoritative preachers of that gospel) and authorised-by-Christ apostolic interpretation of the gospel (i.e. the epistles). The canon of Scripture is the Christ-centred word of the Lord for all who will receive it as the divine message of God, the Word of God written. The authority of Scripture, that is, is the authority of its divine Author.
Thus questioning the authority of Scripture in the life of the church places the questioner in a difficult relationship with Scripture and with God revealed in Christ through this specific 'Word of Christ'. Does the questioner deny the authority of Scripture as the authority of God? Is the questioner denying that the church has properly recognised and received this word?
Further, there tends to be a logical absurdity when Christians question the authority of Scripture. For every Christian is a Christian precisely because they have received a portion of Scripture as authoritative. Every Christian acts under at least one aspect of that authority. This one believes that at communion the bread becomes the body of Christ: why? Because Jesus himself said [in Scripture], 'This is my body.' That one believes that God loves everyone: why? Because we read [in Scripture] that 'God is love.' Another asserts dogmatically that we should be merciful and kind to all we meet: why? Because Christ said so [in Scripture].
On what basis then does a Christian questioning the authority of Scripture determine that some parts are unquestionably authoritative while others are undoubtedly irrelevant to the church today? I have no idea.
Addendum: for an erudite and challenging approach to authority, which I think is in heated agreement with this post and its predecessor, read Bryden Black's article, Lion's Work, here.