The Church has encouraged prayer for the dead from the earliest times as an act of Christian charity. “If we had no care for the dead,” Augustine noted, “we would not be in the habit of praying for them.”
The theological underpinning of the feast is the acknowledgment of human frailty. Because few of us achieve perfection in this life but go to the grave still scarred with traces of sinfulness, a period of purification seems necessary before a soul may come face-to-face with God. The Council of Trent affirmed this purgatory state and taught that the prayers of the living can speed up the process of purification.
Medieval popular belief held that the souls in purgatory could appear on this day in the form of witches, toads, or will-o’-the-wisps. Graveside food offerings were intended to help the dead to rest. Religious observances include public processions or private visits to cemeteries and decorating graves with flowers and lights.