"The sacraments are efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us. The visible rites by which the sacraments are celebrated signify and make present the graces proper to each sacrament. They bear fruit in those who receive them with the required dispositions." (Catechism of the Catholic Church 1131)
All world religions make use of what we call sacraments, but the word sacrament is unique to Christianity. The term itself comes from the classical and early church Latin word sacramentum, which itself has its ties to the Greek term mysterion. In ancient Greece, before Christ walked the earth, whenever people felt the presence of a higher spiritual power interacting with humanity, they referred to that experience as mysterion. This term mysterion is present in the Old Testament as well as in the letters of the New Testament. St. Paul, in his Letter to the Colossians, describes his life work as announcing and bringing to completion this "mystery (mysterion) hidden from ages and generations past." (1:26)
In the late second century, Tertullian of Carthage chose to translate the word mysterion into the Latin word sacramentum. The word sacramentum was a Roman military term for the "Sacred oath" a soldier took when entering the imperial army. Joseph Martos, in his classic work on the history of the sacraments, Doors to the Sacred states:
"In a discussion on the meaning of baptism, Tertullian explained that it was similar to the sacramentum which was administered to Roman recruits when they entered the army. The sacramentum was a religious initiation; so was baptism. It marked the beginning of a new way of life; so did baptism. The sacramentum was an oath of allegiance to the emperor; baptism was a promise of fidelity to Christ."
St. Augustine broadened the use of the term sacramentum to mean not only a religious ceremony but also any "sacred sign." He listed hundreds of "sacraments" including making the sign of the cross, anointing with oil, praying the Nicene Creed. Eventually, the Church came to differentiate between sacraments as ritual ceremonies and sacramentals as objects blessed for the purpose of personal devotion.
The thirteenth century saw a tremendous increase in writings on the sacraments with the Dominicans, Franciscans and Augustinians all weighing in with their theologies. The Lateran Council of 1215 was the first to declare the number of sacraments as seven which later was confirmed at the Council of Trent (1547), which declared, "The sacraments of the new law are seven, no more and no less." (Session VII, Canon 1)
The Catholic understanding of sacrament cannot be understood apart from the concept of grace or "gift of God." Karl Rahner and other modern theologians speak of grace as "God's personal self communication." For this reason, Catholics no longer speak of sacraments "giving grace" so much as the sacraments allowing us to "experience grace."
The Constitution on the Sacred Liturgy, #7 states, "To accomplish so great a work, Christ is always present in his Church, especially in its liturgical celebrations. He is present in the sacrifice of the Mass, not only in the person of his minister...but especially under the Eucharistic elements. By his power he is present in the sacraments so that when a man baptizes it is really Christ himself who baptizes. He is present in the Word, since it is he himself who speaks when the holy Scriptures are read in the Church. He is present lastly, when the Church prays and sings..."
"In the sacraments, we respond to God's self-giving and draw closer not only to God but also to one another in the Church." Richard Gula