“A sacrament is an efficacious sign instituted by Christ to give grace.”
1: efficacious sign
First, a sign points to something real beyond itself. The sacraments are the most perfect signs — they are efficacious signs — because the visible signs effect the invisible realities they signify (see CCC 1127). For example, in baptism, the visible sign of washing with water effects the invisible reality of purification from sins & new birth in divine life.
Sacramental signification is threefold (example given for Baptism):
- Past — “commemorative” — the death of Christ on the cross (Rom 6:4).
- Present – “demonstrative” – supernatural transformation in Christ (1 Pet 3:21, Gal 3:27).
- Future – “prophetic” – eternal glory with Christ (Mark 16:16).
2: instituted by Christ
Scripture tells us that Christ determined what special graces were to be conferred by means of external rites: for some sacraments (e.g. baptism, the Eucharist) He determined minutely (in specie) the matter and form: for others He determined only in a general way (in genere) that there should be an external ceremony, by which special graces were to be conferred, leaving to the Apostles or to the Church the power to determine whatever He had not determined, e.g. to prescribe the matter and form of the Sacraments of Confirmation and Holy Orders.
Reason tells us that all sacraments must be of divine origin: “Since the sanctification of man is in the power of God who sanctifies, it is not in the competency of man to choose the things by which he is to be sanctified, but this must be determined by Divine institution” (St. Thomas Aquinas).
3: to give grace
“Sacraments are like hoses. They are the channels of the living water of God’s grace. Our faith is like opening the faucet. We can open it a lot, a little, or not at all” (Peter Kreeft).
Therefore, sacramental grace is always real, always active, always objective (there is a built-in efficacy of the sacrament properly conferred). At the same time, we receive sacramental grace according to our dispositions.