Thanks to all who posted responses to my question below. When I asked, "What's the main point of the Bible..." below, the Westminster Shorter Catechism question four was lurking in the back of my mind: "What do the scriptures principally teach?" "The scriptures principally teach what man is to believe concerning God, and what duty God requires of man.
A few weeks ago, we read that question in church, and it struck me that the answer given by the catechism is sorely lacking because it doesn't mention Jesus. Apart from him, what do we really know about God? Isn't it in seeing him, in knowing him, that we see and know the Father? If he had never come as God's fullest and final revelation of himself to us, would we have any basis for believing all the other stuff we believe about God? I think that Paul's argument in 1 Cor. 15 is that if Jesus hadn't come as the last Adam, and been raised back to life from the grave, we'd have no hope at all. Also, if the Son makes the Father known, and if all the treasures of wisdom and knowledge are in Christ (Col. 2:3), then it seems that apart from Jesus we know nothing of God.
The main point of the Bible:
in 3 words: Jesus, the God-man. (OK, so I'm using a hyphen to sneak in a 4th word. Sorry.)
in 20 words: God's fullest revelation of himself to us is Jesus, the Word, full of grace and truth, bringing salvation and judgement.