Why is baptism referred to as a Sacrament of Initiation?

Answer 1

It is called a sacrament of initiation because once you receive it, you become a member of the Catholic Church.

Catholic AnswerBecause it is the first sacrament received without which you cannot receive any of the others.

Answer 2

Catholic AnswerThe sacraments of initiation (Baptism, Confirmation, and the Most Holy Eucharist) are the intiation and very basis of the Christian life. Without at least baptism, there is no Christian life at all. Confirmation "completes" baptism, and the Most Holy Eucharist is the very Body and Blood, Soul and Divinity, of Our Blessed Lord, Jesus Christ, Himself, in the form of food to nourish our souls and bodies spiritually.

from The Catechism of the Catholic Church, second edition, English translation 1994

1212 The sacrament os Christian initiation - Baptism, Confirmation, and the Eucharist - lay the foundations of every Christian life. "The sharing in the divine nature given to men through the grace of Christ bears a certain likeness to the origin, development, and nourishing of natural life. The faithful are born anew by Baptism, strengthened by the sacrament of Confirmation, and receive in the Eucharist the food of eternal life. By means of these sacrament os Christian initiation, they thus receive in increasing measure the treasures of the divine life and advance toward the perfection of charity." (Paul VI, apostolic constitution, Divinae consortium naturae: Acta Apostolicae Sedis 63 {1971})

Answer 3

Roman Catholic AnswerThere are three Sacraments of Initiation:

from Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980

Baptism: in which a person is cleansed of all sin and reborn and sanctified in Christ to everlasting life.

Confirmation: in which a person is strengthened by the Holy Spirit in order that they steadfastly profess the faith and faithfully live up to their profession.

The Most Holy Eucharist: which is the true Body and Blood of Our Blessed Lord, Jesus Christ, who is really and substantially present under the appearances of bread and wine in order to offer Himself in the sacrifice of the Mass and to be received as spiritual food in Holy Communion.