Objection 1. It would seem that matrimony still comes under a precept. For a precept is binding so long as it is not recalled. But the primary institution of matrimony came under a precept, as stated in the text (Sent. iv, D, 26); nor do we read anywhere that this precept was recalled, but rather that it was confirmed (Matthew 19:6): "What... God hath joined together let no man put asunder." Therefore matrimony still comes under a precept.
Objection 2. Further, the precepts of natural law are binding in respect of all time. Now matrimony is of natural law, as stated above (Article 1). Therefore, etc.
Objection 3. Further, the good of the species is better than the good of the individual, "for the good of the State is more Godlike than the good of one man" (Ethic. i, 2). Now the precept given to the first man concerning the preservation of the good of the individual by the act of the nutritive power is still in force. Much more therefore does the precept concerning matrimony still hold, since it refers to the preservation of the species.
Objection 4. Further, where the reason of an obligation remains the same, the obligation must remain the same. Now the reason why men were bound to marry in olden times was lest the human race should cease to multiply. Since then the result would be the same, if each one were free to abstain from marriage, it would seem that matrimony comes under a precept.
On the contrary, It is written (1 Corinthians 7:38): "He that giveth not his virgin in marriage doth better [Vulgate: 'He that giveth his virgin in marriage doth well, and he that giveth her not doth better']," namely than he that giveth her in marriage. Therefore the contract of marriage is not now a matter of precept.
Further, no one deserves a reward for breaking a precept. Now a special reward, namely the aureole, is due to virgins [Cf. 96, 5]. Therefore matrimony does not come under a precept.
I answer that, Nature inclines to a thing in two ways. In one way as to that which is necessary for the perfection of the individual, and such an obligation is binding on each one, since natural perfections are common to all. In another way it inclines to that which is necessary for the perfection of the community; and since there are many things of this kind, one of which hinders another, such an inclination does not bind each man by way of precept; else each man would be bound to husbandry and building and to such offices as are necessary to the human community; but the inclination of nature is satisfied by the accomplishment of those various offices by various individuals. Accordingly, since the perfection of the human community requires that some should devote themselves to the contemplative life to which marriage is a very great obstacle, the natural inclination to marriage is not binding by way of precept even according to the philosophers. Hence Theophrastus proves that it is not advisable for a wise man to marry, as Jerome relates (Contra Jovin. i).
Reply to Objection 1. This precept has not been recalled, and yet it is not binding on each individual, for the reason given above, except at that time when the paucity of men required each one to betake himself to the begetting of children.
The Replies to objections 2 and 3 are clear from what has been said.
Reply to Objection 4. Human nature has a general inclination to various offices and acts, as already stated. But since it is variously in various subjects, as individualized in this or that one, it inclines one subject more to one of those offices, and another subject more to another, according to the difference of temperament of various individuals. And it is owing to this difference, as well as to Divine providence which governs all, that one person chooses one office such as husbandry, and another person another. And so it is too that some choose the married life and some the contemplative. Wherefore no danger threatens.
Source: Summa Theologica (New Advent)