From the Catechism

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."

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."

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 1499, 1514, 1532)

Anointing of the Sick

What is the Anointing of the Sick and when is it to be offered? These are great questions whose answers are rooted in Scripture:

Is anyone among you sick? He should summon the priests of the church, and they should pray over him and anoint (him) with oil in the name of the Lord, and the prayer of faith will save the sick person, and the Lord will raise him up. If he has committed any sins, he will be forgiven. (James 5:14-15)

So, the priests, called presbyters in antiquity, were called upon to anoint those who were ill. Furthermore, we see that the one being anointed was prayed for and sins forgiven. In the course of centuries, this sacrament started being used only for those who were dying. It took on the name extreme unction to indicate that this action was the the last anointing. All too frequently people still associate being anointed with being near the state of death. On the contrary, the Second Vatican Council renewed the most ancient theology and practice to once again offer it for anyone who is seriously ill or about to have surgery, etc.

The Last Rites

This event is a series of rituals culminating in the giving of the Eucharist as Viaticum. The Catechism of the Catholic Church puts it well:

In addition to the Anointing of the Sick, the Church offers those who are about to leave this life the Eucharist as viaticum. Communion in the body and blood of Christ, received at this moment of "passing over" to the Father, has a particular significance and importance. It is the seed of eternal life and the power of resurrection, according to the words of the Lord: "He who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day."[140] The sacrament of Christ once dead and now risen, the Eucharist is here the sacrament of passing over from death to life, from this world to the Father

Thus, just as the sacraments of Baptism, Confirmation, and the Eucharist form a unity called "the sacraments of Christian initiation," so too it can be said that Penance, the Anointing of the Sick and the Eucharist as viaticum constitute at the end of Christian life "the sacraments that prepare for our heavenly homeland" or the sacraments that complete the earthly pilgrimage.

(CCC 1524-25)