Summa Theologica I-II, q. 102: Of the Causes of the Ceremonial Precepts
And all these things had reasonable causes, both literal, in so far as they were ordained to the worship of God for the time being, and figurative, in so far as they were ordained to foreshadow Christ: as we shall see by taking them one by one.
Reply to Objection 1The chief literal reason for circumcision was in order that man might profess his belief in one God. And because Abraham was the first to sever himself from the infidels, by going out from his house and kindred, for this reason he was the first to receive circumcision. This reason is set forth by the Apostle (Rom. 4:9, seqq.) thus: "He received the sign of circumcision, a seal of the justice of the faith which he had, being uncircumcised"; because, to wit, we are told that "unto Abraham faith was reputed to justice," for the reason that "against hope he believed in hope," i.e. against the hope that is of nature he believed in the hope that is of grace, "that he might be made the father of many nations," when he was an old man, and his wife an old and barren woman. And in order that this declaration, and imitation of Abraham's faith, might be fixed firmly in the hearts of the Jews, they received in their flesh such a sign as they could not forget, wherefore it is written (Gn. 17:13): "My covenant shall be in your flesh for a perpetual covenant." This was done on the eighth day, because until then a child is very tender, and so might be seriously injured; and is considered as something not yet consolidated: wherefore neither are animals offered before the eighth day. And it was not delayed after that time, lest some might refuse the sign of circumcision on account of the pain: and also lest the parents, whose love for their children increases as they become used to their presence and as they grow older, should withdraw their children from circumcision. A second reason may have been the weakening of concupiscence in that member. A third motive may have been to revile the worship of Venus and Priapus, which gave honor to that part of the body. The Lord's prohibition extended only to the cutting of oneself in honor of idols: and such was not the circumcision of which we have been speaking.
The figurative reason for circumcision was that it foreshadowed the removal of corruption, which was to be brought about by Christ, and will be perfectly fulfilled in the eighth age, which is the age of those who rise from the dead. And since all corruption of guilt and punishment comes to us through our carnal origin, from the sin of our first parent, therefore circumcision was applied to the generative member. Hence the Apostle says (Col. 2:11): "You are circumcised" in Christ "with circumcision not made by hand in despoiling of the body of the flesh, but in the circumcision of" Our Lord Jesus "Christ."
Reply to Objection 2The literal reason of the paschal banquet was to commemorate the blessing of being led by God out of Egypt. Hence by celebrating this banquet they declared that they belonged to that people which God had taken to Himself out of Egypt. For when they were delivered from Egypt, they were commanded to sprinkle the lamb's blood on the transoms of their house doors, as though declaring that they were averse to the rites of the Egyptians who worshipped the ram. Wherefore they were delivered by the sprinkling or rubbing of the blood of the lamb on the door-posts, from the danger of extermination which threatened the Egyptians.
Now two things are to be observed in their departure from Egypt: namely, their haste in going, for the Egyptians pressed them to go forth speedily, as related in Ex. 12:33; and there was danger that anyone who did not hasten to go with the crowd might be slain by the Egyptians. Their haste was shown in two ways. First by what they ate. For they were commanded to eat unleavened bread, as a sign "that it could not be leavened, the Egyptians pressing them to depart"; and to eat roast meat, for this took less time to prepare; and that they should not break a bone thereof, because in their haste there was no time to break bones. Secondly, as to the manner of eating. For it is written: "You shall gird your reins, and you shall have shoes on your feet, holding staves in your hands, and you shall eat in haste": which clearly designates men at the point of starting on a journey. To this also is to be referred the command: "In one house shall it be eaten, neither shall you carry forth of the flesh thereof out of the house": because, to wit, on account of their haste, they could not send any gifts of it.
The stress they suffered while in Egypt was denoted by the wild lettuces. The figurative reason is evident, because the sacrifice of the paschal lamb signified the sacrifice of Christ according to 1 Cor. 5:7: "Christ our pasch is sacrificed." The blood of the lamb, which ensured deliverance from the destroyer, by being sprinkled on the transoms, signified faith in Christ's Passion, in the hearts and on the lips of the faithful, by which same Passion we are delivered from sin and death, according to 1 Pet. 1:18: "You were. . . redeemed. . . with the precious blood. . . of a lamb unspotted." The partaking of its flesh signified the eating of Christ's body in the Sacrament; and the flesh was roasted at the fire to signify Christ's Passion or charity. And it was eaten with unleavened bread to signify the blameless life of the faithful who partake of Christ's body, according to 1 Cor. 5:8: "Let us feast. . . with the unleavened bread of sincerity and truth." The wild lettuces were added to denote repentance for sins, which is required of those who receive the body of Christ. Their loins were girt in sign of chastity: and the shoes of their feet are the examples of our dead ancestors. The staves they were to hold in their hands denoted pastoral authority: and it was commanded that the paschal lamb should be eaten in one house, i.e. in a catholic church, and not in the conventicles of heretics.
Reply to Objection 3Some of the sacraments of the New Law had corresponding figurative sacraments in the Old Law. For Baptism, which is the sacrament of Faith, corresponds to circumcision. Hence it is written (Col. 2:11,12): "You are circumcised. . . in the circumcision of" Our Lord Jesus "Christ: buried with Him in Baptism." In the New Law the sacrament of the Eucharist corresponds to the banquet of the paschal lamb. The sacrament of Penance in the New Law corresponds to all the purifications of the Old Law. The sacrament of Orders corresponds to the consecration of the pontiff and of the priests. To the sacrament of Confirmation, which is the sacrament of the fulness of grace, there would be no corresponding sacrament of the Old Law, because the time of fulness had not yet come, since "the Law brought no man [Vulg.: 'nothing'] to perfection" (Heb. 7:19). The same applies to the sacrament of Extreme Unction, which is an immediate preparation for entrance into glory, to which the way was not yet opened out in the Old Law, since the price had not yet been paid. Matrimony did indeed exist under the Old Law, as a function of nature, but not as the sacrament of the union of Christ with the Church, for that union was not as yet brought about. Hence under the Old Law it was allowable to give a bill of divorce, which is contrary to the nature of the sacrament.
Reply to Objection 4As already stated, the purifications of the Old Law were ordained for the removal of impediments to the divine worship: which worship is twofold; viz. spiritual, consisting in devotion of the mind to God; and corporal, consisting in sacrifices, oblations, and so forth. Now men are hindered in the spiritual worship by sins, whereby men were said to be polluted, for instance, by idolatry, murder, adultery, or incest. From such pollutions men were purified by certain sacrifices, offered either for the whole community in general, or also for the sins of individuals; not that those carnal sacrifices had of themselves the power of expiating sin; but that they signified that expiation of sins which was to be effected by Christ, and of which those of old became partakers by protesting their faith in the Redeemer, while taking part in the figurative sacrifices.