John Milbank is one of the big names in modern theology, although sadly, like many trendy thinkers, actually trying to understand what he's on about is a bit like wading through treacle. Still, I thought it was worth trying to distill some of his treacly ideas about the four senses of scripture for your delectation, so here goes.
Milbank argues that medieval biblical exegesis was influenced by the fact that lots of the people who wrote commentaries on Scripture also wrote commentaries on Dionysius the Areopagite. Now, for Dionysius, the symbols of Christian liturgy participated in the ordered structure of creation, which in turn reflected the nature and character of the infinite God, and, as a result, was overflowing with multiple and varied meaning.
Because the words of scripture pointed to this richly symbolic world, it became to be seen as "oceanum mysteriosum Dei, ut sic loquar labyrinthum" (My Latin's pretty poor, but I think that means something like "the ocean of the mysteries of God" and then something about a labyrinth of speaking. Help me, Latin scholars!) - whatever the subtleties of that phrase, the basic idea is that within the words of Scripture are endless depths and layers and intricacies of meaning in there. Umberto Eco (most famous for his novel The Name of the Rose, a theological murder mystery) argues that the four senses of scripture weren't meant to open up a greater variety of interpretations of scripture, but actually to reduce the number of possible ways of reading the Bible, by limiting it to generally accepted traditions of interpretation.
Now, Milbank thinks that one of the things about Christ is that he embodies the endless possibilities within God. He thinks that Christ is the head and body of the Church in the sense that he kicks off a new way of living 'in Christ', but also right from the start contains all the possibilities which the Church then goes on to embody. All the different ways that the Church and Christians have embodied Christ and lived out the good news of the kingdom of God were potentially contained in Christ from the beginning, and there's no way we'll ever fully understand everything that Christ means, because to do that, we'd have to have a complete view of everything that both Jesus and the Church have done and will do in his name. To be a Christian, thinks Milbank, is actually to contribute something to the person, meaning, and body of Christ.
As a result, Milbank thinks that when we read Scripture allegorically, tropologically, and anagogically as well as literally, it becomes possible for us to read it as the story of our lives rather than just a story about dead people (and I know, Jesus is still alive, but that's Milbank's point: if we can't read the Bible in these ways, we can't read our own lives as part of the story of Jesus, so he effectively is dead anyway).
Milbank then goes on to argue that, as Protestants started (at least theoretically) to reject the possibility of reading Scripture in these multiple ways, focusing on literal interpretations and getting back to the New Testament Church, what they actually did was to shut down possibilities for reading Jesus into their own lives, and as a result, what they did was to move their understanding of salvation away from the idea of participation in Christ towards the offer of abstract grace which would somehow pay off our abstract debt to God. In addition, says Milbank, this shrinking of the range of acceptable readings of Scripture did away with the role of the Church: just as reading went from encountering symbols which pointed beyond themselves to things in the world, multiple meanings, and God himself to an activity in which the individual directly confronted the literal meaning of the text, so the sense of the individual being caught up into the rich, messy and complicated symbolisms of the rituals, actions, liturgies and symbols of the Church was abandoned in favour of a vision of the individual directly confronting God, alone with their conscience.
I hope that makes sense. If you, too, feel like you are drowing in treacle reading this, please shout and I'll see if I can destickify you a bit...