The Catholic Church is one big happy family.
It includes Church Triumphant (the saints and angels in heaven), Church Suffering (the holy souls in purgatory), and Church Militant (the baptized faithful on earth who keep up the fight of good against evil). As a family we can help each other on our pilgrimage of faith. We do so by performing works of charity, offering up inconveniences and sufferings, praying for one another, and finally, almsgiving.
Praying for one another is not a specifically Catholic custom. All Christians perform this sacred duty. We do so informally through our personal prayers or formally during the Mass, specifically the General Intercessions. Catholics believe this prayer goes beyond the grave.
The saints are alive and well in paradise. They are God’s closest friends and are enjoying the Beatific Vision. The desire of the saints is for everyone to enjoy this vision. Catholics often call upon the saints to continue their prayers to God in heaven. Catholics will “offer up” their prayers on behalf of other people or for the holy souls in purgatory.
Purgatory is a temporary state. It is not a place. It will come to a close at the end of the world. When a person dies and goes to purgatory, he is guaranteed to go to heaven. The person dies as a friend of God, but is not fully prepared to meet the Lord for all eternity. The person recognizes some imperfections or attachments that must be purged before entering the Pearly Gates. While the person in Purgatory cannot do anything but wait, Church Triumphant and Church Militant can.
On Earth, Masses are regularly celebrated for the departed loved ones, so that the Precious Blood of Jesus at the Holy Sacrifice may be applied to a soul in purgatory. In addition, Catholics may “offer up” their inconveniences or sufferings in order to release a soul to heaven. Any good work that we do is added to the Treasury of Merit won for us by our Blessed Savior on the wood of the cross. We can tap into this treasury and give it to someone in need by performing a penance or work of charity.
The next time you miss your bus, are stuck in traffic, or are late for an appointment, don’t blow your top—”offer it up” for a holy soul in purgatory.