The seven sacraments · Question 2.2
“If the Holy Spirit already came at baptism, why is Confirmation needed as well?”

Confirmation — a mission strengthened in the Holy Spirit
The Church's answer: Confirmation is not a repair job on a defective baptism. It is the sacrament in which the Holy Spirit particularly strengthens the life baptism began and completes it, so that faith is witnessed to in the Church and in the world. Baptism, Confirmation and the Eucharist are not in competition; together they make one journey of Christian initiation.
If they press further: “Same Spirit, so where's the difference?” — The same Spirit gives different sacramental gifts. Receiving life, and being sent to live that life strongly within a mission, are distinct — though never separated.
In one sentence: “Confirmation isn't a second helping of the Holy Spirit — it's the sacrament where the Spirit strengthens the life of baptism for witness and mission.”