The souls in purgatory died in the mercy of God, this is why they are called holy; however, because they still had attachment to sin at the time of their death, they must undergo a spiritual purification of their souls before they are able to fully love God with their whole heart, mind, and soul for all eternity. Those in purgatory cannot pray for themselves, this is why they are also called “poor” souls. They can no longer merit anything for themselves and they must rely entirely on others to pray and make sacrifices on their behalf. It is an act of charity that we can give for those we have known and loved, for our ancestors who gave us life, for those who were our benefactors, for those whose memory is lost, and for those who have no one else to pray for them.
At americaneedsfatima.org read a collection of “Quotes from Saints about Holy Souls in Purgatory.” Then at catholiccompany.com read suggestions of “20 Ways to Pray for the Holy Souls in Purgatory.”