Halloween or All Hallow’s Eve, was first made a feast by Pope Gregory IV in 835 and later instituted as a Christian celebration in connection with All Saints Day (NOV 1) by Pope Boniface IV, All Hallows Eve was intended to observe the Christian conquest of evil.
It was believe that the veil between the spirit world and the natural world became so thin at this time that evil spirits could come forth and steal the souls of good people. To confuse the spirits, people were to dress up as demons and witches. By suggesting that they do otherwise, misguided religious leaders are leading souls to the devil.