In the ancient world, the Celts, led by the Druids, celebrated the festival of Samhain on the night of October 31-November 1. This celebration was also known as the “festival of the dead”. On this night, the people gave thanks to their gods for the recent harvest and prepared for the coming winter. They also thought that, on this night, the world of the dead came so close to the world of the living that the souls of the departed and evil spirits were allowed to roam about the earth. The Celts were so afraid that they offered sacrifices to the god of the dead and left gifts of food out for any spirits that might pass by.
When Christianity came to this part of the world, the festival was given up in favor of the observance of All Saints’ Day. In the ancient world, every major Christian feast began after a prayer vigil on the evening before. Many denominations still observe this practice. Consequently, the festivities of All Saints’ Day began on the evening of October 31 or “All Hallow’s Eve”. The modern name “Halloween” developed in 16th century Scotland as an abbreviation of the original name.
The celebration on November 1 also led to the feast of All Souls on November 2. The Catholic Church and several other denominations reserve November 2 as a special day of prayer for the souls of the departed that they might rest in peace.
It should be noted that Halloween and All Saints’ Day did not develop solely because the Church wanted to Christianize a pagan holiday. All Saints’ Day has existed since the 4th century. For many years, however, it was celebrated on the first Sunday after the feast of Pentecost. During the 7th century, the feast was moved to May 13 because this was the anniversary of the dedication of a chapel in Saint Peter’s Basilica to All the Saints. About 200 years later, it was permanently moved to November 1.
The reason for this final change was, not so much because of the traditional pagan holidays around this time of year, but rather because of common sense. For centuries, thousands of Christians made a pilgrimage to Rome and to the chapel of All the Saints on the yearly feast. However, it was quickly realized that it would be much easier to feed the pilgrims if the celebration took place after the harvest rather than during the middle of Spring.
Although All Hallow’s Eve was meant, in part, to be a Christianized version of the festival of Samhain, the placement of its date was purely coincidental.
Sources: EWTN online article “Halloween and Its Origination”
Pinto, Matthew and Jason Evert “Did Jesus Have a Last Name?”