2 MACCABEES, 12:45-46:
"And because he considered that they who had fallen asleep with godliness, had great grace laid up for them. It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins."
The poor souls who await their entrance into Heaven while they languish and are purified in the Fire of Divine Love. As these souls can no longer help themselves through the practice of prayer and good works, the Church encourages us to spiritually assist them by offering prayers and sacrifices on their behalf to obtain their eternal rest.
It is said that the Holy Souls are aware of their spiritual benefactors and will gratefully intercede for those who have assisted with their release from Purgatory. They could also be powerful advocates in the hour of death, as there have been many reports of how the Holy Souls have appeared to their devoted benefactors in the final moments of life, both to encourage and escort them into the joys of Paradise.
For details on the Church's ancient teachings on Purgatory, check out this link from the online Catholic Encyclopedia: www.newadvent.org/cathen/12575a.htm .
Let us remember our Lord's words told to St. Gertrude the Great , that the following prayer would release 1,000 Souls from Purgatory each time it is said. The prayer was extended to include living sinners, which would alleviate the indebtedness accrued to them during their lives.
"Eternal Father, I offer Thee the Most Precious Blood of Thy Divine Son, Jesus, in union with the Masses said throughout the World today, for all the Holy Souls in Purgatory, for sinners everywhere, for sinners in the Universal Church, those in my own home and within my family, Amen."