Objection 1. It would seem that the ceremonial precepts have not a literal, but merely a figurative cause. For among the ceremonial precepts, the chief was circumcision and the sacrifice of the paschal lamb. But neither of these had any but a figurative cause: because each was given as a sign. For it is written (Genesis 17:11): "You shall circumcise the flesh of your foreskin, that it may be a sign of the covenant between Me and you": and of the celebration of the Passover it is written (Exodus 13:9): "It shall be as a sign in thy hand, and as a memorial before thy eyes." Therefore much more did the other ceremonial precepts have none but a figurative reason.
Objection 2. Further, an effect is proportionate to its cause. But all the ceremonial precepts are figurative, as stated above (Question 101, Article 2). Therefore they have no other than a figurative cause.
Objection 3. Further, if it be a matter of indifference whether a certain thing, considered in itself, be done in a particular way or not, it seems that it has not a literal cause. Now there are certain points in the ceremonial precepts, which appear to be a matter of indifference, as to whether they be done in one way or in another: for instance, the number of animals to be offered, and other such particular circumstances. Therefore there is no literal cause for the precepts of the Old Law.
On the contrary, Just as the ceremonial precepts foreshadowed Christ, so did the stories of the Old Testament: for it is written (1 Corinthians 10:11) that "all (these things) happened to them in figure." Now in the stories of the Old Testament, besides the mystical or figurative, there is the literal sense. Therefore the ceremonial precepts had also literal, besides their figurative causes.
I answer that, As stated above (Article 1), the reason for whatever conduces to an end must be taken from that end. Now the end of the ceremonial precepts was twofold: for they were ordained to the Divine worship, for that particular time, and to the foreshadowing of Christ; just as the words of the prophets regarded the time being in such a way as to be utterances figurative of the time to come, as Jerome says on Hosea 1:3. Accordingly the reasons for the ceremonial precepts of the Old Law can be taken in two ways. First, in respect of the Divine worship which was to be observed for that particular time: and these reasons are literal: whether they refer to the shunning of idolatry; or recall certain Divine benefits; or remind men of the Divine excellence; or point out the disposition of mind which was then required in those who worshipped God. Secondly, their reasons can be gathered from the point of view of their being ordained to foreshadow Christ: and thus their reasons are figurative and mystical: whether they be taken from Christ Himself and the Church, which pertains to the allegorical sense; or to the morals of the Christian people, which pertains to the moral sense; or to the state of future glory, in as much as we are brought thereto by Christ, which refers to the anagogical sense.
Reply to Objection 1. Just as the use of metaphorical expressions in Scripture belongs to the literal sense, because the words are employed in order to convey that particular meaning; so also the meaning of those legal ceremonies which commemorated certain Divine benefits, on account of which they were instituted, and of others similar which belonged to that time, does not go beyond the order of literal causes. Consequently when we assert that the cause of the celebration of the Passover was its signification of the delivery from Egypt, or that circumcision was a sign of God's covenant with Abraham, we assign the literal cause.
Reply to Objection 2. This argument would avail if the ceremonial precepts had been given merely as figures of things to come, and not for the purpose of worshipping God then and there.
Reply to Objection 3. As we have stated when speaking of human laws (96, A1,6), there is a reason for them in the abstract, but not in regard to particular conditions, which depend on the judgment of those who frame them; so also many particular determinations in the ceremonies of the Old Law have no literal cause, but only a figurative cause; whereas in the abstract they have a literal cause.
Source: Summa Theologica (New Advent)