What will happen to the souls in purgatory during the Final Judgment?
Here’s a reply from Father Reginald Martin:
When he describes the Last Judgment (see M. 25:31-46), Jesus tells us humankind will face only two fates: heaven and hell. Purgatory, St. Augustine reminds us, like any salutary penitential practices we now embrace, will cease to exist with the Judgment: “Let purification punishments be counted on only before that last and terrible judgment.”
What will happen to souls in purgatory when Jesus announces the Last Judgment? What, for that matter, will happen to persons still alive when he comes? In the Creed, we profess belief in Christ who will “judge the living and the dead.” These words presuppose both that some individuals will be alive at the time of the Last Judgment, and that Jesus has taken their reparation into account.
We must assume the same for the souls in purgatory. Our belief in purgatory assures us it is a state ordained to qualify a soul to enter the eternal happiness of heaven. “Immediately on the conclusion of the purification [the soul] will be assumed into the bliss of heaven” (Ludwig Ott, “Fundamentals of Catholic Dogma”). Our faith must trust God has considered the extent of the souls’ purification when determining the time of the Last Judgment.