1 A Little History
The Authority of God
A good starting point is to recognize that the authority of Scripture comes from the authority of God. For some Wesleyans, this statement is so obvious that it does not need mentioned. In fact, for some it may be difficult even to know what a distinction between the two might look like.
For example, a person may read the Bible like you would watch a video recording of the people and events in the Bible. When God speaks in the story, you hear the exact words that God said, and even when someone else is speaking in the Bible, you are still pretty much hearing God speak directly to you. For this person, the Bible is hardly Paul's words to the Corinthians or Isaiah's words to Israel but it is overwhelmingly God's word to everyone in all times and places.
So if one word of the Bible had an error, then it would call into question every single word of the Bible. To this person, God has more or less dictated the words of the Bible, and it would make God a liar if even one word was not true. It would call into question his entire character as truthful.
For other Wesleyans, it is crucial to emphasize the derivative nature of the authority of Scripture in relation to the authority of God. All Wesleyans agree that the authority of Scripture comes from the authority of God. But for some Wesleyans, this distinction is very important. For example, someone might notice that there are lots of groups that believe the Bible is without error but whose interpretations of the Bible differ widely from Wesleyans. For example, Jehovah's Witnesses, who believe that Jesus was only a god, not the God, believe the Bible is inerrant.  David Koresh believed the Bible was inerrant, who led his cult followers to Waco, Texas only to die in a suicidal fire.
It is thus only the Bible, rightly interpreted, that has the authority of God. We remember from Matthew 4 and Luke 4 that Satan can use the Bible for evil. Indeed, those calling themselves Christians have repeatedly used the Bible to justify evil and sinful intentions--murder, oppression, hate. Look under the masks of the KKK and you would have found many self-righteous pastors and church leaders. Look into Hitler's Germany and you would have found many a pastor who will not likely be in the kingdom of God.
To modify Jesus' words slightly, "If I testify about myself, my testimony is not true. There is another who testifies in my favor" (John 5:31-32, NIV). Christians throughout the centuries have regularly believed that it is the Bible as illuminated by the Spirit that is the word of God, and Christians have often suggested that a person without faith may not be able to hear it. You can read the Bible as a mere historical source and not hear or experience it as Christian Scripture.
The New Testament itself suggests that the word of God requires "ears to hear" (Mark 4:23). 1 Peter 1:10-12 pictures the prophets and angels incredibly curious of what their words might turn out to mean about the Christ, a reflection of the fact that the christological meaning of the Old Testament was not always obvious to the Old Testament prophets themselves. It was more often a "spiritual" or fuller sense to the Old Testament words of the prophets than their literal or plain sense. God's plan for the Gentiles was thus a mysterious development, one not anticipated (Eph. 3:5). It is thus the Bible, rightly interpreted, that has the authority of God.
The more we are aware of the books of the Bible themselves as moments of revelation in history, the more important it is to recognize that it is not the books themselves but the God to which they give witness who is all in all. The Bible is the word of God, but Christ is the Word of God. Anything else approaches idolatry, to make an image of Christ into the object of worship, to worship the creation rather than the Creator, to put human words above the divine Word.
God leaves an element of mystery in the revelation of the Bible so that we do not think the book alone is sufficient but we are driven to Christ himself. The Bible does not give us all the answers so we will trust in him. Indeed, in the end it is essential that we not view the Bible as object, as an end-in-itself for us to master. Rather, God seeks to master us through Scripture.  The authority of Scripture is not so much the voice of Scripture speaking to us, but the action of God on us through Scripture.
 Joel Green mentions this in Seized by Truth.
 A point that Green strongly tries to bring out in Seized.