Summa theologica
Reply to Objection 1: Poetry makes use of metaphors to produce a representation, for it is natural to man to be pleased with representations. But sacred doctrine makes use of metaphors as both necessary and useful.
Reply to Objection 2: The ray of divine revelation is not extinguished by the sensible imagery wherewith it is veiled, as Dionysius says (Coel. Hier. i); and its truth so far remains that it does not allow the minds of those to whom the revelation has been made, to rest in the metaphors, but raises them to the knowledge of truths; and through those to whom the revelation has been made others also may receive instruction in these matters. Hence those things that are taught metaphorically in one part of Scripture, in other parts are taught more openly. The very hiding of truth in figures is useful for the exercise of thoughtful minds and as a defense against the ridicule of the impious, according to the words "Give not that which is holy to dogs" (Mat. 7:6).
Reply to Objection 3: As Dionysius says, (Coel. Hier. i) it is more fitting that divine truths should be expounded under the figure of less noble than of nobler bodies, and this for three reasons. Firstly, because thereby men's minds are the better preserved from error. For then it is clear that these things are not literal descriptions of divine truths, which might have been open to doubt had they been expressed under the figure of nobler bodies, especially for those who could think of nothing nobler than bodies. Secondly, because this is more befitting the knowledge of God that we have in this life. For what He is not is clearer to us than what He is. Therefore similitudes drawn from things farthest away from God form within us a truer estimate that God is above whatsoever we may say or think of Him. Thirdly, because thereby divine truths are the better hidden from the unworthy.
Whether in Holy Scripture a word may have several senses?
Objection 1: It seems that in Holy Writ a word cannot have several senses, historical or literal, allegorical, tropological or moral, and anagogical. For many different senses in one text produce confusion and deception and destroy all force of argument. Hence no argument, but only fallacies, can be deduced from a multiplicity of propositions. But Holy Writ ought to be able to state the truth without any fallacy. Therefore in it there cannot be several senses to a word.
Objection 2: Further, Augustine says (De util. cred. iii) that "the Old Testament has a fourfold division as to history, etiology, analogy and allegory." Now these four seem altogether different from the four divisions mentioned in the first objection. Therefore it does not seem fitting to explain the same word of Holy Writ according to the four different senses mentioned above.
Objection 3: Further, besides these senses, there is the parabolical, which is not one of these four.
On the contrary, Gregory says (Moral. xx, 1): "Holy Writ by the manner of its speech transcends every science, because in one and the same sentence, while it describes a fact, it reveals a mystery."
I answer that, 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. So, whereas in every other science things are signified by words, this science has the property, that the things signified by the words have themselves also a signification. Therefore that first signification whereby words signify things belongs to the first sense, the historical or literal. That signification whereby things signified by words have themselves also a signification is called the spiritual sense, which is based on the literal, and presupposes it. Now this spiritual sense has a threefold division. For as the Apostle says (Heb. 10:1) the Old Law is a figure of the New Law, and Dionysius says (Coel. Hier. i) "the New Law itself is a figure of future glory." Again, in the New Law, whatever our Head has done is a type of what we ought to do. Therefore, so far as the things of the Old Law signify the things of the New Law, there is the allegorical sense; so far as the things done in Christ, or so far as the things which signify Christ, are types of what we ought to do, there is the moral sense. But so far as they signify what relates to eternal glory, there is the anagogical sense. Since the literal sense is that which the author intends, and since the author of Holy Writ is God, Who by one act comprehends all things by His intellect, it is not unfitting, as Augustine says (Confess. xii), if, even according to the literal sense, one word in Holy Writ should have several senses.