Confirmation is a sacrament of mature Christian commitment and a deepening of baptismal gifts. Like Baptism and Eucharist, it is a Sacrament of Initiation for Catholics and a Sacrament of faith in God's fidelity to us.
Before Jesus was put to death, He promised His followers that He would send His Spirit to comfort and strengthen them. True to His promise, the Holy Spirit was poured out on them on Pentecost, forty days after His resurrection from the dead. The Sacrament of Confirmation is our own Pentecost. When we are confirmed, we receive the Holy Spirit, through the anointing with oil and the laying on of hands by the bishop or a priest appointed by him.
When we receive this sacred seal we show that we belong to God. By their anointing, the prophets, kings and priests of the Old Testament were elevated to a special position in their service of God. So it is with us when we receive the holy oil on our foreheads; we become part of the priesthood of all believers, witnesses to Christ and heirs to His throne.