No.1316 and 1317, page 333 of the Catechism of the Catholic Church: The Celebration of the Christian Mystery; Libreria Editrice Vaticana: Urbi Et Orbi Communications:
Confirmation perfects Baptismal grace; it is the sacrament which gives the Holy Spirit in order to root us more deeply in the divine filiation, incorporate us more firmly into Christ, strengthen our bond with the Church, associate us more closely with her mission, and help us bear witness to the Christian faith in words accompanied by deeds.
Confirmation, like Baptism, imprints a spiritual mark or indelible character on the Christian's soul; for this reason one can receive this sacrament only once in one's life.
From the Baltimore Catechism No. 2; Benziger Brothers, Inc. and Tan Books and Publishers, Inc. No. 337 and 339.
Q. What are the effects of Confirmation?
A. The effects of Confirmation are an increase of sanctifying grace, the strengthening of our faith, the gifts of the Holy Ghost, and imprints a lasting character on the soul.
Q. What is the character of Confirmation?
A. The character of Confirmation is a spiritual and indelible sign which marks the Christian as a soldier in the army of Christ.