St. Thomas Aquinas: Commentary 
On the First Epistle to the Corinthians

“I will not hide from you the secrets (sacraments) of God, but will trace out her course from the beginning of creation and make the knowledge of her clear and will not pass by the truth” (Wis 6:22).
1. – The word “sacrament” can be taken in two senses: sometimes it means something secret, particularly in regard to sacred things; and sometimes it means the sign of a sacred thing, in the sense of being its image and cause. It is in this second sense that we speak of the seven sacraments: baptism, confirmation, Eucharist, penance, extreme unction, orders and matrimony. Furthermore, the first sense is then included in this second sense, for a divine power is secretly at work in these sacraments of the Church, as Augustine says.
2. – Consequently, these sacraments of God should not be concealed but laid bare to Christ’s faithful by their teachers and prelates for three reasons.
First, because this redounds to God’s honor: “It is good to hide the secret of the King, but honorable to reveal and confess the works of the Lord” (Tob 12:7).
Secondly, because this is needed for the salvation of men, who could lapse into despair from not
knowing them, for Wisdom (2:22) says that some men “did not know the secret purposes of God, nor hope for the wages of holiness,” because men are purified by the sacraments and prepared for receiving the wages of holiness.
Thirdly, because this is a duty of teachers and prelates as pointed out by the Apostle: “To me, though I am the very least of the saints, this grace was given, to make all men see what is the plan of the mystery hidden for ages in God” (Eph 3:8).
Thus the above text discloses to us the subject manner of this epistle, in which the Apostle discusses the sacraments of the Church. For since in the epistle to the Romans he had discussed God’s grace, which works in the seven sacraments, here in the first epistle to the Corinthians he discusses the sacraments themselves and in the second epistle to the Corinthians the ministers of the sacraments.
Let us turn, therefore, to the text.