When Christianity spread to parts of Europe, instead of trying to abolish these pagan customs, people tried to introduce ideas which reflected a more Christian world-view. Halloween has since become a confusing mixture of traditions and practices from pagan cultures and Christian tradition.
By A.D. 43, Romans had conquered the majority of Celtic territory. During their rule of the Celtic lands, Roman festivals were combined with the traditional Celtic celebration of Samhain. The Romans observed the holiday of Feralia, intended to give rest and peace to the departed. Participants made sacrifices in honor of the dead, offered up prayers for them, and made oblations to them. Another festival was a day to honor Pomona, the Roman goddess of fruit and trees. The symbol of Pomona is the apple and the incorporation of this celebration into Samhain probably explains the tradition of "bobbing" for apples that is practiced today on Halloween.
As the influence of Christianity spread into Celtic lands, in the 7th century, Pope Boniface IV introduced All Saints' Day, a time to honor saints and martyrs, to replace the pagan festival of the dead. It was observed on May 13. In 834, Gregory III moved All Saint's Day from May 13 to Nov. 1 and for Christians, this became an opportunity for remembering before God all the saints who had died and all the dead in the Christian community. Oct. 31 thus became All Hallows' Eve ('hallow' means 'saint').
Sadly, though, many of the customs survived and were blended in with Christianity. Numerous folk customs connected with the pagan observances for the dead have survived to the present.
In 1517, a monk named Martin Luther honored the faithful saints of the past by choosing All Saints Day (November 1) as the day to publicly charge the Church heirarchy with abandoning biblical faith. This became known as "Reformation Day," a fitting celebration of the restoration the same biblical faith held by the saints throughout church history.