Today is the Commemoration of All the Faithful Departed, also known as All Souls Day. The church consists of all baptized people who have ever existed except for those now in hell; the rest of us are here on earth (the Church Militant), in heaven (the Church Triumphant), or in Purgatory (the Church Penitent).
"All baptized people" includes most Protestants, of course, but Protestants generally do not believe in Purgatory. And as a result, they don't pray for their dead. I find it poignant to consider people in the Church Penitent whose loved ones on earth do not pray for their purification to be complete. Here is a prayer for the forgotten souls in Purgatory:
Lord, hear the forgotten souls in Purgatory. Purify them and bring them to your side to sing your praises forever. Amen.