Christ the physician 

 
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" 104 and that the Kingdom of God is close at hand. Jesus has the power not only to heal, but also to forgive sins; 105 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. 
Catechism of the Catholic Church (CCC) 1503
 

A sacrament of the sick 

 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. 
CCC 1511

 

Who can receive the Sacrament?

The Anointing of the Sick "is not a sacrament for those only who are at the point of death. Hence, as soon as anyone of the faithful begins to be in danger of death from sickness or old age, the fitting time for him to receive this sacrament has certainly already arrived."  
 
 If a sick person who received this anointing recovers his health, he can in the case of another grave illness receive this sacrament again. If during the same illness the person's condition becomes more serious, the sacrament may be repeated. It is fitting to receive the Anointing of the Sick just prior to a serious operation. The same holds for the elderly whose frailty becomes more pronounced. 
CCC 1514-1515

One can also receive this sacrament prior to surgery.

 

Effects of the Sacrament

The special grace of the sacrament of the Anointing of the Sick has as its effects: 
- the uniting of the sick person to the passion of Christ, for his own good and that of the whole Church; 
- the strengthening, peace, and courage to endure in a Christian manner the sufferings of illness or old age; 
- the forgiveness of sins, if the sick person was not able to obtain it through the sacrament of Penance; 
- the restoration of health, if it is conducive to the salvation of his soul; 
- the preparation for passing over to eternal life. 
CCC 1532