Thomas Aquinas

I will not hide the mysteries of God from you, etc., Wisdom VI, 24. The term "sacrament" is customarily taken in two ways. For sometimes "sacrament" is said of any secret whatsoever, and especially concerning sacred matters; sometimes "sacrament" is said of the sign of a sacred thing, in such a way that it both bears its image and exists as its cause, according to which we speak of the seven sacraments of the Church, namely Baptism, confirmation, the Eucharist, penance, extreme unction, order, and matrimony. In this latter signification of "sacrament," indeed, the first signification is also contained; for in these sacraments of the Church, divine power more secretly works salvation, as Augustine says. These sacraments of God, therefore, the prelate, or teacher of the Church, ought not to hide from the faithful of Christ but to make manifest, for three reasons. First indeed, because this pertains to the honor of God, according to that word of Tobit XII, 7: it is good to hide the sacrament of a king, but to reveal and confess the works of God is honorable. Second, because this pertains to the salvation of men, who through ignorance of these things could fall into despair, just as it is said of certain ones in Wisdom II, 22, that they did not know the sacraments of God, nor did they hope for the reward of justice, because through the sacraments men are purified, so that they may be prepared to receive the reward of justice. Third, because this pertains to the owed office of a prelate or teacher, according to that word of Ephesians III, 8: to me, the least of all the saints, this grace was given, to enlighten all as to what is the dispensation of the sacrament hidden from the ages in God. Thus, therefore, the aforesaid words show us the subject matter of this epistle, in which the Apostle deals with the sacraments of the Church. For whereas in the epistle to the Romans he had commended the grace of God, which works in the sacraments of the Church: here, that is, in the first epistle to the Corinthians, he deals with the sacraments of the Church themselves; but in the second, with the ministers of the sacraments. Let us, then, first look at the text.