The prophets of the Old Testament foretold that God's Spirit would rest upon the Messiah to sustain his mission. Their prophecy was fulfilled when Jesus the Messiah was conceived by the Spirit and born of the Virgin Mary. The Holy Spirit descended on Jesus on the occasion of his baptism by John. Jesus' entire mission took place in communion with the Spirit. Before he died, Jesus promised that the Spirit would be given to the Apostles and to the entire Church. After his death, he was raised by the Father in the power of the Spirit.
Before Jesus ascended into heaven, he told his disciples to wait in Jerusalem so that they could receive the baptism of the Holy Spirit (Acts 1:5). When about 120 of Jesus' disciples were gathered the Holy Spirit came in the form of wind and fire. Filled with the Holy Spirit, the disciples understood that God was anointing them for a special mission (Acts 2).
The early Christians made sure, then, that whenever they brought people into the Church, they would baptize them with water and then anoint them with oil. Why oil? Oil had been used in the Old Testaments to anoint priests, prophets, and kings. The early Christians realized that their community was "a chosen race, a royal priesthood, a holy nation" (1 Pet 2:9). Each new member was anointed with oil after being baptized with water.
In the early Church Baptism and Confirmation were celebrated in a single ceremony. It is still done this way in the churches of the East. In the Roman Catholic Church, the Church of the West, the two sacraments gradually separated. The Church in the West wanted the bishop to complete a person's initiation. As the Church grew and the bishops ministered over ever larger territories, the bishop could not be present for every Baptism. So began the custom of gathering groups of baptized Catholics together later so that the bishop could confirm them all at one time. In the process over time the reception of the Eucharist came before the celebration of Confirmation.
Confirmation is one of the sacraments of the Church. Together with Baptism and the Eucharist, it constitutes the set of "the sacraments of Christian initiation," that is, sacraments whose reception is necessary for the fullness of the grace we receive in Baptism. The sacrament of Confirmation unites the Church more intimately and enriches her with a special strength of the Holy Spirit. Thus, those who receive it are obliged to spread and defend the faith by word and deed, as true witnesses of Christ.
Confirmation deepens our baptismal life that calls us to be missionary witnesses of Jesus Christ in our families, neighbourhoods, society, and the world. We receive the message of faith in a deeper and more intensive manner with great emphasis given to the person of Jesus Christ, who asked the Father to give the Holy Spirit to the Church for building up the community in loving service.
Receiving the Sacrament of Confirmation, The Christian becomes more closely united with Christ and the Christian's relationship with God is made stronger. The Gifts of the Holy Spirit are strengthened: wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of the Lord. In this way the Christian is equipped to become a better witness to Christ in the world. With the strengthening of the Gifts of the Holy Spirit the Christian is able to accept new responsibilities for witnessing Jesus to the world.
A bishop is the usual celebrant of the Sacrament of Confirmation. During the celebration of Confirmation, the bishop extends his hands over those to be confirmed and calls upon God: "Send your Holy Spirit upon them to be their helper and guide." Then each person to be confirmed is anointed with chrism on the forehead as the bishop says, "Be sealed with the Gift of the Holy Spirit."
Confirmation, like Baptism, imprints on the Christian's soul a spiritual sign or indelible character; this is why this sacrament can only be received once in a lifetime. (CCC, 1302-1305)