Sacraments: a definition
The sacraments are Christ's own gift that provides us with His grace. They are the divine helps which God gives us to enable us: to believe the truths of His faith, to live according to His moral code and to grow in His gift of divine life. The seven sacraments are a fundamental part of the Catholic faith…
The exact definition of a sacrament is that it is "an outward sign instituted by Christ to give grace." There are three distinct ideas contained in that short definition:
The outward signs are God's way of treating us like the human beings we are. He conveys His unseen grace into our spiritual souls through material symbols which our physical bodies can perceive—things and words and gestures. The outward signs of the sacraments have two parts: the "thing" itself which is used (water, oil, etc.), and the words or gestures which give significance to what is being done.
...Instituted by Christ...
We know that no human power could attach an inward grace to an outward sign—not even the divinely guided but humanly applied power of the Church. Only God can do that. Between the time He began His public life and the time He ascended into heaven, Jesus fashioned the seven sacraments. When He ascended into heaven, that put an end to the making of sacraments. The Church cannot institute new sacraments. There never can be more or less than seven, the seven Jesus has given us: Baptism , Confirmation , Holy Eucharist , Reconciliation (Confession or Penance), Anointing of the Sick , Holy Orders , and Matrimony . Jesus did completely specify the matter and form of some of the sacraments—notably Baptism and the Holy Eucharist. But this does not mean that He necessarily fixed the matter and form of all the sacraments down to the last detail. In some instances, His Church specifies in detail the broad matter and form assigned by Christ.
...To give grace...
Coming now to the third element in the definition of a sacrament, we have its essential purpose: "to give grace." What kind of grace do the sacraments give? First and most important of all, they give sanctifying grace . Sanctifying grace is that supernatural life, that sharing-in-God's-own-life that is the result of God's Love, the Holy Spirit, indwelling in the soul.
(This explanatory text is a paraphrase of material found on the BeginningCatholic.com website, assembled originally from material adapted and abridged from Father Leo Trese's book, The Faith Explained . That work is Nihil Obstat : Louis J. Putz, C.S.C., University of Notre Dame. Imprimatur : Leo A. Pursley, D.D., Bishop of Fort Wayne, Indiana.)