Work of mercy

Bringing souls out of purgatory is one of the 14 works of mercy.

2447 The works of mercy are charitable actions by which we help our neighbor in his bodily and spiritual needs (cf. Is 58, 6-7; Hb 13, 3). Instructing, counseling, consoling and comforting are spiritual works of mercy, as are forgiving and suffering with patience. The corporal works of mercy consist especially in feeding the hungry, sheltering the homeless, clothing the naked, visiting the sick and the imprisoned, and burying the dead (cf. Mt 25,31-46). Among these works, almsgiving to the poor (cf. Tb 4, 5-11; Yes 17, 22) is one of the main testimonies of fraternal charity; it is also a practice of justice that pleases God (cf. Mt 6:2-4): "He who has two coats, let him share them with him who has none; he who has enough to eat, let him do likewise" (Lc 3, 11). "Give rather in alms what you have, and so all things will be pure for you" (Lc 11, 41). "If a brother or sister is naked and destitute of daily sustenance, and one of you says to them, 'Go in peace, be warmed or fed,' but you do not give them what is necessary for the body, what good is it?" (St 2:15-16; cf Jn 3, 17).

St. John Paul II, Catechism of the Catholic Church.

The works of mercy are these:

944. What are the principal corporal works of mercy? -`

The principal corporal works of mercy are:

1st Visiting and caring for the sick.

2. To feed the hungry.

3rd To give drink to the thirsty.

4.ª To give lodging to the pilgrim.

5th Dressing in the nude.

6th To redeem the captive; and

7th Burying the dead.

945. What are the main spiritual works of mercy?

The principal spiritual works of mercy are:

1st To teach those who do not know.

2nd Giving good advice to those who need it.

3rd Correct the one who errs.

4th Forgiveness of insults.

5. Consoling the sad.

6th To suffer with patience the defects of others; and

7º To pray to God for the living and the deceased.

Large Catechism of St. Pius X.

The best prayer for the dead is the one that takes them out of purgatory. And the best way to get them out of purgatory is to offer a plenary indulgence for one of them.

801. What is plenary indulgence? - Plenary indulgence is that which forgives all the temporal punishment due for sins. For this reason, if one were to die after gaining it, he would go straight to heaven, without passing through purgatory.

The Large Catechism of St. Pius X

The point is that instead of gaining the plenary indulgence for oneself, one offers it for a soul in purgatory.