Catechism of the Catholic Church §1522 — excerpt
An ecclesial grace. the sick who receive this sacrament, "by freely uniting themselves to the passion and death of Christ," "contribute to the good of the People of God."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: LG 11 # 2