By the sacred anointing of the sick and the prayer of the priests the whole Church commends those who are ill to the suffering and glorified Lord, that he may raise them up and save them. And indeed she exhorts them to contribute to the good of the People of God by freely uniting themselves to the Passion and death of Christ.".
Illness and suffering have always been among the gravest problems confronted in human life. In illness, man experiences his powerlessness, his limitations, and his finitude. Every illness can make us glimpse death.

Christ's compassion toward the sick and his many healings of every kind of infirmity are a resplendent sign that "God has visited his people"  and that the Kingdom of God is close at hand. Jesus has the power not only to heal, but also to forgive sins;  he has come to heal the whole man, soul and body; he is the physician the sick have need of.   His compassion toward all who suffer goes so far that he identifies himself with them: "I was sick and you visited me."  His preferential love for the sick has not ceased through the centuries to draw the very special attention of Christians toward all those who suffer in body and soul. It is the source of tireless efforts to comfort them.

The Church believes and confesses that among the seven sacraments there is one especially intended to strengthen those who are being tried by illness, the Anointing of the Sick:

This sacred anointing of the sick was instituted by Christ our Lord as a true and proper sacrament of the New Testament. It is alluded to indeed by Mark, but is recommended to the faithful and promulgated by James the apostle and brother of the Lord.

source: http://www.vatican.va/archive/ccc_css/archive/catechism/p2s2c2a5.htm