From The Cathechism of the Catholic Church (link to the Vatican Website)
“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.”98
1526 “Is any among you sick? Let him call for the presbyters of the Church, and let them pray over him, anointing him with oil in the name of the Lord; and the prayer of faith will save the sick man, and the Lord will raise him up; and if he has committed sins, he will be forgiven” (Jas 5:14-15).
1531 The celebration of the Anointing of the Sick consists essentially in the anointing of the forehead and hands of the sick person (in the Roman Rite) or of other parts of the body (in the Eastern rite), the anointing being accompanied by the liturgical prayer of the celebrant asking for the special grace of this sacrament.
1532 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.