Interpreting metaphors (and covenants): continuity and discontinuity

Miss Clarke's discussion of the interpretation of the poetry of the Song of Songs has provoked me to blog this:

Rev'd Dr Peter Leithart is discussing 'Sacramental Hermeneutics and the Ceremonies of Israel', arguing that Old Testament "ceremonial laws" (though the category is clumsy) play a part in regulating the ceremonial life of the New Testament church, with both continuity and discontinuity. Such an approach requires us to be "able to pick out those features of the two ceremonies [of Old and New Testaments] which are common" to both. He continues:

As stated, it appears to be a mystical and well-nigh impossible undertaking, but we perform similar operations all the time. We know, for instance, that Solomon's similie comparing his beloved's eyes to "doves behind your veil" (Song of Songs 4:1) does not mean a) the woman's eyes are feathery, b) the woman's eyes are pure white, c) the woman's eyes are equipped with small claws, d) the woman's eyes can fly, e) the woman's eyes each have two dark eyes of their own, f) the woman's eyes have a beak, or any of a hundred other possible analogies. How do we know this? It is difficult to say, but we do. And it is eaqually difficult to say exactly what the analogy is in this case: how are a woman's eyes like doves? That question has no straightforward or simple answer, but that does not make the comparison nonensical. Discovering appropriate analogies between baptism and circumcision, Passover and Eucharist, is much easier. The point is that we navigate through similie and metaphor and analogy every day, without a second thought.

in The Case for Covenant Communion (Athanasius Press, 2006) p117