By the sacrament of Confirmation, the baptized are more perfectly bound to the Church and are enriched with a special strength of the Holy Spirit. Hence they are, as true witnesses of Christ, more strictly obliged to spread and defend the faith by word and deed."
[Catechism of the Catholic Church, 1285]
Confirmation is the sacrament in which God completes the graces of baptism, deepening the mark of belonging to Him in the soul. The outpouring of the Holy Spirit, when received in a life of faith, empowers us to live the Christian life well - something we simply could never do on our own. Confirmation is not an "adult choice to be Catholic," but rather it is allowing God to choose us and give us the gifts of the Holy Spirit in order to practice the Catholic faith in every aspect of our lives and witness to Christ in every situation.