Catechism of the Catholic Church

Union with the passion of Christ. By the grace of this sacrament the sick person receives the strength and the gift of uniting himself more closely to Christ's Passion: in a certain way he is consecrated to bear fruit by configuration to the Savior's redemptive Passion. Suffering, a consequence of original sin, acquires a new meaning; it becomes a participation in the saving work of Jesus. (1535, 1499)