Sacraments: a definition
The sacraments are chosen instruments of divine power. The exact definition of a sacrament is that it is "an outward sign instituted by Christ to give grace."
We can see three distinct ideas contained in that short definition: Outward sign Instituted by Christ To give grace .
Let's examine exactly what each of these three ideas means:
Outward signs...
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.
...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 marvelous supernatural life, that sharing-in-God's-own-life that is the result of God's Love, the Holy Spirit, indwelling in the soul.
Baptism brings sanctifying grace for the first time. Baptism opens the soul to the flow of God's love, and establishes union between the soul and God.
The sacrament of Reconciliation and annointing of the sick are healing sacraments.
The other sacraments — Confirmation, Holy Eucharist, Marriage give an increase in sanctifying grace. They deepen and intensify the spiritual life of grace which already pulsates through the soul. As each additional sacrament is received (and repeated, when it can be) the level of spiritual vitality rises in the soul—somewhat as the brightness of a fire increases as you add more fuel.