The reasoning behind this stems from the notion that when a soul leaves the body, it is not entirely cleansed from minor sins, however, through the:
"power of prayer and self-denial, the faithful left on earth may be able to help these souls gain the
Beatific Vision they seek, bringing the soul eternal sublime happiness."
In the 7th and 8th centuries, a prayer The Office of the Dead was read out in churches on All Souls' Day. Other rituals include the offering of Requiem Mass for the dead, visiting family graves and reflecting on lost loved ones.