The 'Sacrament of Anointing of the Sick' is one that many people look at as the least of the sacraments, and yet, it is the one which most obviously perpetuates the earthly ministry of Jesus: He went about healing the sick.
Even when Jesus sent his disciples out on their mission, he commissioned them to do likewise: "preach the kingdom of God and heal the sick." (LK 9:1ff)
The disciples did not stop their healing mission after the departure of Jesus. Acts narrates some of the miraculous healings that occurred in the early days of the church. Since then, the healing ministry has been maintained at three diverse levels.
In the first level, there is prayer for healing (for oneself and for others). Where people pray with lively faith, healings do sometimes occur, sometimes very remarkable ones.
Secondly, there is a charism of healing with which some people are given a special power to heal. St. Paul speaks clearly of this charism in I Corinthians 12:9 and 30. For many centuries, it seemed as though this gift were given exclusively to the saints (which is no doubt part of the reason why they are so often invoked in prayers for healing). The Reformation churches rejected this charism along with veneration of the saints. In the nineteenth and twentieth centuries, however, there has been a rediscovery of the gift of healing by Protestants and Catholics alike. Among Catholics, the Charismatic Renewal has led to a new realization that the gift of healing is not confined to the saints but may be simply a charism equipping a person for a special ministry to the sick.
Finally, there is the sacrament of Anointing, in which the sick person is anointed with oil blessed by the local bishop for this purpose. Although in the form of a prayer, it is not merely a prayer for healing. As a sacrament, it has an intrinsic efficacy to bring about what it signifies. Neither does in involve any extraordinary charism; it is part of the ordinary ministry of any priest.
The apostles, from their very first mission, healed the sick by anointing them with oil. Later on, the Letter of James gave the following instructions, which have been followed by the Church ever since: "Is any one of you sick? He should call for the elders of the church to pray over him and anoint him with oil in the name of the Lord. And the prayer offered in faith will make the sick person well; the Lord will raise him up. If he has sinned, he will be forgiven." (James 4:14f)
The effects of the sacrament are carefully delineated in the Ritual of Paul VI: "This sacrament gives the grace of the Holy Spirit to those who are sick: by this grace the whole person is helped and saved, sustained by trust in God and strengthened against the temptations of the Evil One and against anxiety over death. Thus the sick person is able not only to bear suffering bravely, but also to fight against it. A return to physical health may follow the reception of this sacrament if it will be beneficial to the sick person's salvation."
Spiritual Healing can not be left out. There is often a great calm that comes over someone who has been anointed, they feel the hand of God upon them, comforting them, and assuring them, that God is with them.