At confirmation we receive the gifts of the Holy Spirit and confirm our baptismal promises. Greater awareness of the grace of the Holy Spirit is conferred through the anointing of chrism oil and the laying on of hands by the Bishop.
Confirmation perfects Baptismal grace; it is the sacrament which gives the Holy Spirit in order to root us more deeply in the divine filiation, incorporate us more firmly into Christ, strengthen our bond with the Church, associate us more closely with her mission, and help us bear witness to the Christian faith in words accompanied by deeds. (CCC 1316)
Through the Sacrament of Confirmation we renew our baptismal promises and commit to living a life of maturity in the Christian faith. As we read in the Lumen Gentium (the Dogmatic Constitution of the Church) from the Second Vatican Council:
Bound more intimately to the Church by the sacrament of confirmation, [the baptized] are endowed by the Holy Spirit with special strength; hence they are more strictly obliged to spread and defend the faith both by word and by deed as true witnesses of Christ. (no. 11)
Scriptural Foundation for Confirmation
In the Acts of the Apostles we read of the coming of the Holy Spirit on Pentecost. While baptism is the sacrament of new life, confirmation gives birth to that life. Baptism initiates us into the Church and names us as children of God, whereas confirmation calls us forth as God’s children and unites us more fully to the active messianic mission of Christ in the world.
After receiving the power of the Holy Spirit at Pentecost, the Apostles went out and confirmed others, showing confirmation to be an individual and separate sacrament: Peter and John at Samaria (Acts 8:5-6, 14-17) and Paul at Ephesus (Acts 19:5-6). Also the Holy Spirit came down on Jews and Gentiles alike in Caesarea, prior to their baptisms. Recognizing this as a confirmation by the Holy Spirit, Peter commanded that they be baptized (cf. Acts 10:47).
For on him the Father, God, has set his seal. (John 6:27)
It is evident from its celebration that the effect of the Sacrament of Confirmation is the special outpouring of the Holy Spirit as once granted to the apostles on the day of Pentecost.
From this fact, Confirmation brings an increase and deepening of baptismal grace:
it roots us more deeply in the divine filiation which makes us cry, "Abba! Father!" (Romans 8:15);
it unites us more firmly to Christ;
it increases the gifts of the Holy Spirit in us;
it renders our bond with the Church more perfect;
it gives us a special strength of the Holy Spirit to spread and defend the faith by word and action as true witnesses of Christ, to confess the name of Christ boldly, and never to be ashamed of the Cross:
Recall then that you have received the spiritual seal, the spirit of wisdom and understanding, the spirit of right judgment and courage, the spirit of knowledge and reverence, the spirit of holy fear in God's presence. Guard what you have received. God the Father has marked you with his sign; Christ the Lord has confirmed you and has placed his pledge, the Spirit, in your hearts.
The Sacrament of Confirmation as described by Fr. Raphael Mary of the Catholic Newman Center at the University of Washington.