The Tradition holds that Scripture has many senses. I found really striking what St Thomas does with this: "The author of Holy Writ is God, in whose power it is to signify His meaning, not by words only (as man also can do), but also by things themselves." In other words, it seems that the Angelic Doctor thinks that the words of Scripture directly only have a literal meaning (which of course isn't the "literalistic meaning"; the literal meaning of an assertoric text is that proposition which is asserted in the text; as Aquinas says, "When Scripture speaks of God's arm, the literal sense is not that God has such a member"). The non-literal meaning is not a meaning of the words of Scripture, but it is a meaning of the realities signified with the words understood in their literal meaning. Thus, the description of the Israelites' crossing of the sea in the Book of Exodus has as its meaning that the Israelites cross the sea. This text signifies a historical event—the Israelites' crossing of the sea. And the further meanings, such as a future baptism in Christ, are had not by the text, but by the historical event itself. The events of salvation history are thus a text, and the non-literal meaning of Scripture is thus not a meaning of the text of Scripture, but a meaning of salvation history itself.
I really like this. If the non-literal meanings of the text were really meanings of the text as such, it is hard to see what would distinguish them from the literal meaning. One alternative is to say that the non-literal meanings are intended by God but not by the human author. But if so, then that makes the human author less fully the author of the text, and it makes God an embedder of secret messages in the text. On Aquinas' view, the human author gets to be fully the author of the text, even if the human author does not grasp any of the non-literal meanings. For the non-literal meanings aren't really meanings of the text. (And there is nothing unusual about the events described by a historian having a meaning going far beyond that which the historian sees in them. But these meanings are of the events, not of the history book.) Moreover, this shifts us from being unduly book-centered. Those who experienced the Sinai event were not in principle worse off than the readers reading about the event. But if the additional meanings were meanings of the text and not of the event itself, then those who experienced the Sinai event were in principle worse off than those who read about it.
All this gives a strong sense to the idea that the non-literal meanings of Scripture depend on the literal meaning. For if the Israelites did not in fact cross the sea, then there is no historical event of the crossing of the sea to bear any of the non-literal meanings. The words of Scripture don't signify a future baptism—they signify a crossing of the sea. The crossing of the sea would signify a future baptism, but since the crossing didn't take place on this hypothesis, that is irrelevant.
Moreover, if Aquinas' idea is right—and I think it is right as the notion that God writes not just in words but in historical events is deeply embedded in the Christian tradition—then the theologian who denies the various miracle stories but hopes to save a non-literal meaning is in even greater trouble. For while we assert by speech and not by silence (unless we set up a special convention—"If I say nothing, assume I agree"), we implicate both by speech and by silence. If the Israelites did not in fact cross the sea, not only is the crossing of the sea not there to bear a non-literal meaning, but the non-existence of the crossing of the sea—i.e., God's refraining from causing a crossing of the sea—carries an implicature that we should be cognizant of. But the implicature carried by refraining from an utterance s is typically (though not always, but a special case would need to be made out that the present case is such an exception) opposed to the meaning that s would have had. So the theologian who reads the miracle stories ahistorically, if Aquinas is right, may well make God out to be implicating something opposed to the non-literal meaning that the theologian hopes to find there.