Baptism, the Eucharist, and the sacrament of Confirmation together constitute the “sacraments of Christian initiation,” whose unity must be safeguarded. It must be explained to the faithful that the reception of the sacrament of Confirmation is necessary for the completion of baptismal grace. For “by the sacrament of Confirmation, [the baptized] are more perfectly bound to the Church and are enriched with the 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.” (CCC 1285)
“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 placed his pledge, the Spirit, in your hearts.”
St. Ambrose, De myst. 7, 42: PL 16, 402-403