They are called the sacraments of initiation because they are three sacraments to be received by a person whereby their relationship and connection to the Church is fully established.
One is fully initiated into the faith community by receiving all three of these sacraments. Membership has its privileges, as well as its duties and obligations. Fully initiated members are expected to come to Mass every weekend and to go to confession.
After the Roman Emperor Constantine issued the Edict of Milan (313 AD), the Church was able to come above ground from the catacombs and worship freely. It could expand its missionary activities and lead people to conversion. Also, after the Emperor converted, it became fashionable to be a Christian. In fact, the opposite form of persecution took place against the pagans. With this mass entrance into the one holy Catholic and Apostolic Church, a program of preparation had to be developed. Our present-day convert program, known as the Rite of Christian Initiation of Adults, is based on this early time in our Christian history.
Adult converts were not permitted into the church proper—only into the atrium. They would witness the beginning of the Mass, or the liturgy of the Word, from the entrance to the Church. After the homily, the candidates would be dismissed for further instruction while the liturgy of the faithful or Eucharist continued. It was called “faithful” because only the baptized could attend. Today, candidates in RCIA sit in the church proper; after the prayers of the faithful and before the liturgy of the Eucharist, they are dismissed for further instruction.
It is at the Easter Vigil that these candidates are invited to stay for the whole Mass. At this Eucharistic celebration, they will receive the sacraments of Baptism (for those who are not baptized), Confirmation, and first Holy Communion. After reception, they are fully initiated members in the Catholic Church. For those who are baptized as infants or children, the sacraments of initiation are staggered over a ten-year period. After Baptism, children are prepared for first Communion at the age of seven. Part of the preparation is the reception of the sacrament of Penance.
After age ten, but usually before age eighteen, children are prepared to receive Confirmation. Upon reception of this sacrament, they are fully initiated and considered full members of the Church. The sacraments of initiation are referred to as such because that is what they were intended to be: initiations of the faithful.