Confirmation (from Latin, meaning “strengthening”) is one of the three sacraments of Christian initiation, a personal Pentecost experience. It is not, as is often imagined, a “coming of age” or “reaching maturity” in the faith; in the Eastern Rites of the Church, Confirmation is received by infants. But it does perfect our bond with the Church, which is the Mystical Body of Christ, and it makes us “Soldiers of Christ”, as St. Cyril of Jerusalem wrote in his Catechetical lectures back in the 4th century.
The confirmed Christian is “sealed with the gift the Holy Spirit”, which imparts an indelible character that conforms the person more closely to Christ. The Catechism (#1303) teaches that this sacrament “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.”