Whether the Sacraments are the Cause of Grace?
Objection 1: It seems that the sacraments are not the cause of grace. For it seems that the same thing is not both sign and cause: since the nature of sign appears to be more in keeping with an effect. But a sacrament is a sign of grace. Therefore it is not its cause. Objection 2: Further, nothing corporeal can act on a spiritual thing: since "the agent is more excellent than the patient," as Augustine says (Gen. ad lit. xii). But the subject of grace is the human mind, which is something spiritual. …
Saint Thomas Aquinas—Summa Theologica

Whether There Should be Seven Sacraments?
Objection 1: It seems that there ought not to be seven sacraments. For the sacraments derive their efficacy from the Divine power, and the power of Christ's Passion. But the Divine power is one, and Christ's Passion is one; since "by one oblation He hath perfected for ever them that are sanctified" (Heb. 10:14). Therefore there should be but one sacrament. Objection 2: Further, a sacrament is intended as a remedy for the defect caused by sin. Now this is twofold, punishment and guilt. Therefore two …
Saint Thomas Aquinas—Summa Theologica

Whether the Sacrament of Penance May be Repeated?
Objection 1: It would seem that the sacrament of Penance should not be repeated. For the Apostle says (Heb. 6:4, seqq.): "It is impossible for those, who were once illuminated, have tasted also the heavenly gift, and were made partakers of the Holy Ghost . . . and are fallen away, to be renewed again to penance." Now whosoever have done penance, have been illuminated, and have received the gift of the Holy Ghost. Therefore whosoever sin after doing penance, cannot do penance again. Objection 2: Further, …
Saint Thomas Aquinas—Summa Theologica