The mystery of Holy Unction is also called euchelaeon, which is essentially a transliteration of the Greek ευχέλαιον, and stands for "blessed oil" (ευχή = blessing prayer, έλαιον = oil).
When one is ill and in pain, this can very often be a time of life when one feels alone and isolated. The Sacrament of the Anointing of the Sick, or Holy Unction reminds us that when we are in pain, either physical, emotional, or spiritual, Christ is present with us through the ministry of His Church. He is among us to offer strength to meet the challenges of life, and even the approach of death.
As with Chrismation, oil is also used in this Sacrament as a sign of God's presence, strength, and forgiveness. After the reading of seven Epistle lessons, seven Gospel lessons and the offering of seven prayers, which are all devoted to healing, the priest anoints the body with the Holy Oil. Orthodoxy does not view this Sacrament as available only to those who are near death. It is offered to all who are sick in body, mind, or spirit.
Christ came to the world to “bear our infirmities.” One of the signs of His divine Messiahship was to heal the sick. The power of healing remains in the Church since Christ himself remains in the Church through the Holy Spirit.
The Sacrament of the Unction of the sick is the Church's specific prayer for healing. If the faith of the believers is strong enough, and if it is the will of God, there is every reason to believe that the Lord can heal those who are diseased.
The biblical basis for the Sacrament is found in James 5:14-16:
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. Therefore, confess your sins to one another and pray for one another, that you may be healed.
In ancient Christian literature one may find indirect testimonies of the Mystery of Unction in Saint Irenaeus of Lyons and in Origen. Later there are clear testimonies of it in Saints Basil the Great and John Chrysostom, who have left prayers for the healing of the infirm which entered later into the rite of Unction; and likewise in Saint Cyril of Alexandria. In the fifth century, Pope Innocent I answered a series of questions concerning the Mystery of Unction, indicating in his answers that a) it should be performed "upon believers who are sick"; b) it may be performed also by a bishop, since one should not see in the words of the Apostle, let him call for the presbyters, any prohibition for a bishop to participate in the sacred action; c) this anointment may not be performed "on those undergoing ecclesiastical penance,' because it is a "Mystery,' and to those who are forbidden the other Mysteries, how can one allow only one?
The express purpose of the Sacrament of Holy Unction is healing and forgiveness. Since it is not always the will of God that there should be physical healing, the prayer of Christ that God's will be done always remains as the proper context of the Sacrament. In addition, it is the clear intention of the Sacrament that through the anointing of the sick body the sufferings of the person should be sanctified and united to the sufferings of Christ. In this way, the wounds of the flesh are consecrated, and strength is given that the suffering of the diseased person may not be unto the death of his soul, but for eternal salvation in the resurrection and life of the Kingdom of God.
It is indeed the case that death inevitably comes. All must die, even those who in this life are given a reprieve through healing in order to have more time on the earth. Thus, the healing of the sick is not itself a final goal, but is merely "instrumental" in that it is given by God as a sign of his mercy and as a grace for the further opportunity of man to live for him and for others in the life of this world.
In the case where a person is obviously in the final moments of his earthly life, the Church has special prayers for the "separation of soul and body." Thus, it is clear that the Sacrament of Holy Unction is for the sick–both the physically and mentally sick–and is not reserved for the moment of death. The Sacrament of Unction is not the "last rites" as is sometimes thought; the ritual of the anointing itself in no way indicates that it should be administered merely in "extreme" cases. Holy Unction is the Sacrament of the spiritual, physical, and mental healing of a sick person whatever the nature or the gravity of the illness may be.