The sacrament of Confirmation is necessary for the completion of baptismal grace. CCC 1285

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 apostle on the day of Pentecost.

From this fact, Confirmation brings an increase and deepening of baptismal grace:

• roots us more deeply in the divine filiation which makes us cry, "Abba! Father!"
• unites us more firmly to Christ
• magnifies the gifts of the Holy Spirit in us
• renders our bond with the Church more perfect
• gives us a special strength of the Holy Spirit to spread and defend the faith