The other issue about the plain meaning of the text (see previous post) is the extent to which the New Testament authors presupposed familiarity with the Old Testament, familiarity such that the first hearers of the New testament 'heard' all the allusions there are in it to the Hebrew scriptures and its story.
It is certainly the case today that most of those sitting in the audiences for our sermons are not familiar with the Old Testament. they maybe know a few famous stories, have a favourite Psalm, know that Abraham came before Moses who came before David. But do they know enough top catch Paul's allusions to the sweep of the Old Testament story in Galatians? I doubt it.
When I spoke yesterday of Paul's ideas of fruitfulness coming from the key Old testament image of Israel being the vine not many heads nodded - and a couple of people said to me afterwards that would be going to read Isaiah 5 and 58 with a new interest. I suggested that they also read Jesus' parables of the sower and vineyard as well.
Perhaps this is an argument for doing sermons on recurring themes and images in the Bible. More fundamentally, it raises questions about how we disciple people - whether we're talking about what children in Sunday School are learning or what kind of catechism we offer to new believers. This latter takes into the territory of Alan Kreider's suggestion that baptismal preparation should take a lot longer than we currently allow.
What do people need to know in order to be Christians? Paul stresses that believers need to be growing in knowledge. Is he talking about what we'd call Bible knowledge (however that's acquired in a pre-book culture) or something else?