Objection 1. It seems that the third precept of the decalogue, concerning the hallowing of the Sabbath, is unfittingly expressed. For this, understood spiritually, is a general precept: since Bede in commenting on Luke 13:14, "The ruler of the synagogue being angry that He had healed on the Sabbath," says (Comment. iv): "The Law forbids, not to heal man on the Sabbath, but to do servile works," i.e. "to burden oneself with sin." Taken literally it is a ceremonial precept, for it is written (Exodus 31:13): "See that you keep My Sabbath: because it is a sign between Me and you in your generations." Now the precepts of the decalogue are both spiritual and moral. Therefore it is unfittingly placed among the precepts of the decalogue.
Objection 2. Further, the ceremonial precepts of the Law contain "sacred things, sacrifices, sacraments and observances," as stated above (I-II, 101, 4). Now sacred things comprised not only sacred days, but also sacred places and sacred vessels, and so on. Moreover, there were many sacred days other than the Sabbath. Therefore it was unfitting to omit all other ceremonial observances and to mention only that of the Sabbath.
Objection 3. Further, whoever breaks a precept of the decalogue, sins. But in the Old Law some who broke the observances of the Sabbath did not sin--for instance, those who circumcised their sons on the eighth day, and the priests who worked in the temple on the Sabbath. Also Elias (1 Kings 19), who journeyed for forty days unto the mount of God, Horeb, must have traveled on a Sabbath: the priests also who carried the ark of the Lord for seven days, as related in Joshua 7, must be understood to have carried it on a Sabbath. Again it is written (Luke 13:15): "Doth not every one of you on the Sabbath day loose his ox or his ass... and lead them to water?" Therefore it is unfittingly placed among the precepts of the decalogue.
Objection 4. Further, the precepts of the decalogue have to be observed also under the New Law. Yet in the New Law this precept is not observed, neither in the point of the Sabbath day, nor as to the Lord's day, on which men cook their food, travel, fish, and do many like things. Therefore the precept of the observance of the Sabbath is unfittingly expressed.
On the contrary, stands the authority of Scripture.
I answer that, The obstacles to true religion being removed by the first and second precepts of the decalogue, as stated above (2,3), it remained for the third precept to be given whereby man is established in true religion. Now it belongs to religion to give worship to God: and just as the Divine scriptures teach the interior worship under the guise of certain corporal similitudes, so is external worship given to God under the guise of sensible signs. And since for the most part man is induced to pay interior worship, consisting in prayer and devotion, by the interior prompting of the Holy Ghost, a precept of the Law as necessary respecting the exterior worship that consists in sensible signs. Now the precepts of the decalogue are, so to speak, first and common principles of the Law, and consequently the third precept of the decalogue describes the exterior worship of God as the sign of a universal boon that concerns all. This universal boon was the work of the Creation of the world, from which work God is stated to have rested on the seventh day: and sign of this we are commanded to keep holy seventh day--that is, to set it aside as a day to be given to God. Hence after the precept about the hallowing of the Sabbath the reason for it is given: "For in six days the Lord made heaven and earth... and rested on the seventh day."
Reply to Objection 1. The precept about hallowing the Sabbath, understood literally, is partly moral and partly ceremonial. It is a moral precept in the point of commanding man to aside a certain time to be given to Divine things. For there is in man a natural inclination to set aside a certain time for each necessary thing, such as refreshment of the body, sleep, and so forth. Hence according to the dictate of reason, man sets aside a certain time for spiritual refreshment, by which man's mind is refreshed in God. And thus to have a certain time set aside for occupying oneself with Divine things is the matter of a moral precept. But, in so far as this precept specializes the time as a sign representing the Creation of the world, it is a ceremonial precept. Again, it is a ceremonial precept in its allegorical signification, as representative of Christ's rest in the tomb on the seventh day: also in its moral signification, as representing cessation from all sinful acts, and the mind's rest in God, in which sense, too, it is a general precept. Again, it is a ceremonial precept in its analogical signification, as foreshadowing the enjoyment of God in heaven. Hence the precept about hallowing the Sabbath is placed among the precepts of the decalogue, as a moral, but not as a ceremonial precept.
Reply to Objection 2. The other ceremonies of the Law are signs of certain particular Divine works: but the observance of the Sabbath is representative of a general boon, namely, the production of all creatures. Hence it was fitting that it should be placed among the general precepts of the decalogue, rather than any other ceremonial precept of the Law.
Reply to Objection 3. Two things are to be observed in the hallowing of the Sabbath. One of these is the end: and this is that man occupy himself with Divine things, and is signified in the words: "Remember that thou keep holy the Sabbath day." For in the Law those things are said to be holy which are applied to the Divine worship. The other thing is cessation from work, and is signified in the words (Exodus 20:11), "On the seventh day... thou shalt do no work." The kind of work meant appears from Leviticus 23:3, "You shall do no servile work on that day [Vulgate: 'You shall do no work on that day']." Now servile work is so called from servitude: and servitude is threefold. One, whereby man is the servant of sin, according to John 8:34, "Whosoever committeth sin is the servant of sin," and in this sense all sinful acts are servile. Another servitude is whereby one man serves another. Now one man serves another not with his mind but with his body, as stated above (104, 5,6, ad 1). Wherefore in this respect those works are called servile whereby one man serves another. The third is the servitude of God; and in this way the work of worship, which pertains to the service of God, may be called a servile work. On this sense servile work is not forbidden on the Sabbath day, because that would be contrary to the end of the Sabbath observance: since man abstains from other works on the Sabbath day in order that he may occupy himself with works connected with God's service. For this reason, according to John 7:23, "a man [Vulgate: 'If a man,' etc.] receives circumcision on the Sabbath day, that the law of Moses may not be broken": and for this reason too we read (Matthew 12:5), that "on the Sabbath days the priests in the temple break the Sabbath," i.e. do corporal works on the Sabbath, "and are without blame." Accordingly, the priests in carrying the ark on the Sabbath did not break the precept of the Sabbath observance. On like manner it is not contrary to the observance of the Sabbath to exercise any spiritual act, such as teaching by word or writing. Wherefore a gloss on Numbers 28 says that "smiths and like craftsmen rest on the Sabbath day, but the reader or teacher of the Divine law does not cease from his work. Yet he profanes not the Sabbath, even as the priests in the temple break the Sabbath, and are without blame." On the other hand, those works that are called servile in the first or second way are contrary to the observance of the Sabbath, in so far as they hinder man from applying himself to Divine things. And since man is hindered from applying himself to Divine things rather by sinful than by lawful albeit corporal works, it follows that to sin on a feast day is more against this precept than to do some other but lawful bodily work. Hence Augustine says (De decem chord. iii): "It would be better if the Jew did some useful work on his farm than spent his time seditiously in the theatre: and their womenfolk would do better to be making linen on the Sabbath than to be dancing lewdly all day in their feasts of the new moon." It is not, however, against this precept to sin venially on the Sabbath, because venial sin does not destroy holiness.
Again, corporal works, not pertaining to the spiritual worship of God, are said to be servile in so far as they belong properly to servants; while they are not said to be servile, in so far as they are common to those who serve and those who are free. Moreover, everyone, be he servant or free, is bound to provide necessaries both for himself and for his neighbor, chiefly in respect of things pertaining to the well-being of the body, according to Proverbs 24:11, "Deliver them that are led to death": secondarily as regards avoiding damage to one's property, according to Deuteronomy 22:1, "Thou shalt not pass by if thou seest thy brother's ox or his sheep go astray, but thou shalt bring them back to thy brother." Hence a corporal work pertaining to the preservation of one's own bodily well-being does not profane the Sabbath: for it is not against the observance of the Sabbath to eat and do such things as preserve the health of the body. For this reason the Machabees did not profane the Sabbath when they fought in self-defense on the Sabbath day (1 Maccabees 2), nor Elias when he fled from the face of Jezabel on the Sabbath. For this same reason our Lord (Matthew 12:3) excused His disciples for plucking the ears of corn on account of the need which they suffered. On like manner a bodily work that is directed to the bodily well-being of another is not contrary to the observance of the Sabbath: wherefore it is written (John 7:23): "Are you angry at Me because I have healed the whole man on the Sabbath day?" And again, a bodily work that is done to avoid an imminent damage to some external thing does not profane the Sabbath, wherefore our Lord says (Matthew 12:11): "What man shall there be among you, that hath one sheep, and if the same fall into a pit on the Sabbath day, will he not take hold on it and lift it up?"
Reply to Objection 4. In the New Law the observance of the Lord's day took the place of the observance of the Sabbath, not by virtue of the precept but by the institution of the Church and the custom of Christian people. For this observance is not figurative, as was the observance of the Sabbath in the Old Law. Hence the prohibition to work on the Lord' day is not so strict as on the Sabbath: and certain works are permitted on the Lord's day which were forbidden on the Sabbath, such as the cooking of food and so forth. And again in the New Law, dispensation is more easily granted than in the Old, in the matter of certain forbidden works, on account of their necessity, because the figure pertains to the protestation of truth, which it is unlawful to omit even in small things; while works, considered in themselves, are changeable in point of place and time.
Source: Summa Theologica (New Advent)