Objection 1. It would seem that the goods of marriage are insufficiently enumerated by the Master (Sent. iv, D, 31), namely "faith, offspring, and sacrament." For the object of marriage among men is not only the begetting and feeding of children, but also the partnership of a common life, whereby each one contributes his share of work to the common stock, as stated in Ethic. viii, 12. Therefore as the offspring is reckoned a good of matrimony, so also should the communication of works.
Objection 2. Further, the union of Christ with the Church, signified by matrimony, is the effect of charity. Therefore charity rather than faith should be reckoned among the goods of matrimony.
Objection 3. Further, in matrimony, just as it is required that neither party have intercourse with another, so is it required that the one pay the marriage debt to the other. Now the former pertains to faith according to the Master (Sent. iv, D, 31). Therefore justice should also be reckoned among the goods of marriage on account of the payment of the debt.
Objection 4. Further, in matrimony as signifying the union of Christ with the Church, just as indivisibility is required, so also is unity, whereby one man has one wife. But the sacrament which is reckoned among the three marriage goods pertains to indivisibility. Therefore there should be something else pertaining to unity.
Objection 5. On the other hand, it would seem that they are too many. For one virtue suffices to make one act right. Now faith is one virtue. Therefore it was not necessary to add two other goods to make marriage right.
Objection 6. Further, the same cause does not make a thing both useful and virtuous, since the useful and the virtuous are opposite divisions of the good. Now marriage derives its character of useful from the offspring. Therefore the offspring should not be reckoned among the goods that make marriage virtuous.
Objection 7. Further, nothing should be reckoned as a property or condition of itself. Now these goods are reckoned to be conditions of marriage. Therefore since matrimony is a sacrament, the sacrament should not be reckoned a condition of matrimony.
I answer that, Matrimony is instituted both as an office of nature and as a sacrament of the Church. As an office of nature it is directed by two things, like every other virtuous act. one of these is required on the part of the agent and is the intention of the due end, and thus the "offspring" is accounted a good of matrimony; the other is required on the part of the act, which is good generically through being about a due matter; and thus we have "faith," whereby a man has intercourse with his wife and with no other woman. Besides this it has a certain goodness as a sacrament, and this is signified by the very word "sacrament."
Reply to Objection 1. Offspring signifies not only the begetting of children, but also their education, to which as its end is directed the entire communion of works that exists between man and wife as united in marriage, since parents naturally "lay up" for their "children" (2 Corinthians 12:14); so that the offspring like a principal end includes another, as it were, secondary end.
Reply to Objection 2. Faith is not taken here as a theological virtue, but as part of justice, in so far as faith [fides] signifies the suiting of deed to word [fiant dicta] by keeping one's promises; for since marriage is a contract it contains a promise whereby this man is assigned to this woman.
Reply to Objection 3. Just as the marriage promise means that neither party is to have intercourse with a third party, so does it require that they should mutually pay the marriage debt. The latter is indeed the chief of the two, since it follows from the power which each receives over the other. Consequently both these things pertain to faith, although the Boo of Sentences mentions that which is the less manifest.
Reply to Objection 4. By sacrament we are to understand not only indivisibility, but all those things that result from marriage being a sign of Christ's union with the Church. We may also reply that the unity to which the objection refers pertains to faith, just as indivisibility belongs to the sacrament.
Reply to Objection 5. Faith here does not denote a virtue, but that condition of virtue which is a part of justice and is called by the name of faith.
Reply to Objection 6. Just as the right use of a useful good derives its rectitude not from the useful but from the reason which causes the right use, so too direction to a useful good may cause the goodness of rectitude by virtue of the reason causing the right direction; and in this way marriage, through being directed to the offspring, is useful, and nevertheless righteous, inasmuch as it is directed aright.
Reply to Objection 7. As the Master says (Sent. iv, D, 31), sacrament here does not mean matrimony itself, but its indissolubility, which is a sign of the same thing as matrimony is.
We may also reply that although marriage is a sacrament, marriage as marriage is not the same as marriage as a sacrament, since it was instituted not only as a sign of a sacred thing, but also as an office of nature. Hence the sacramental aspect is a condition added to marriage considered in itself, whence also it derives its rectitude. Hence its sacramentality, if I may use the term, is reckoned among the goods which justify marriage; and accordingly this third good of marriage, the sacrament to wit, denotes not only its indissolubility, but also whatever pertains to its signification.
Source: Summa Theologica (New Advent)