Fright night:

Hallowe'en is one of the natural holidays. More than anything else, it celebrates the end of another growth cycle.  

That can be either good or bad, depending on the harvest. Survival during the winter months ahead depended on a successful growth season. 

The season is celebrated in such parallel feast days as Thanksgiving and Oktoberfest in the northern hemisphere. Both feature plenty of food and drink.

Religious holidays attached to this seasonal celebration include All Saints Day.  Festivities include the ancestors in some Central and South American communities. They are held in cemeteries where families celebrate among the tombs and burial sites of those who went before them. We are told this can get pretty macabre in some locales. 

But why not? It's the recognition of Death, after all. Death is an important part of Life. It is a vital part of evolution. Without it, life would lose its identity..