LOL, it's an old pagan celebration, for entering into the dark evenings, the end of harvest. Pagans would now pray to the man of the woods (green man) the horned god instead of the summer goddess.
Probably for a good hunt to get meat over the winter.
Ancient peoples believed that the spirits of the dead walked among them, hence the lighting of the candles to guide the way.
Christianity wasn't around, or was in it's infancy. There was no such thing as Christ or satan.