The origin of All Hallows’ Eve, “Hallowe’en” for short

Hallows Eve, “Hallowe’en” for short, originated with the Church’s vigil, the evening before All Saints’ Day every November 1st. The full name was All Hallows’ E’en, or Evening.

It therefore was preparatory to celebrating all the holy souls who have now reached their goal of loving God in this life, obeying and serving Him faithfully - fulfillment of eternal loving union with Him in the glory of heaven.

You can see that verbalized in the proper prayer for the vigil:

“Pour forth abundantly upon us of thy mercy, O Lord our God, and grant us grace to follow in their joy in their holy testifying all thy blessed servants the Eve of whose glorious and solemn Commemoration we are keeping.”

Over time, and as a symptom of de-Christianization, other pagan elements crept in so that now some spend the evening celebrating evil, quite obviously the opposite of the intended, with images of devils, witches and other symbols of satanic possession. 

Celtic pagan practices before Christianity included the superstition of dressing as a frightening or evil entity in order to scare the spirits who came with the increased hours of darkness in the Fall. Scaring them away successfully was believed to turn the curse around so that daylight increased toward Spring. 

The most appropriate way to celebrate the vigil of All Saints is by attending the holy Mass designated for the purpose: In Vigilia Omnium Sanctorum ~ Simplex (more about that here: http://mcitl.blogspot.com/2024/10/in-vigilia-omnium-sanctorum-simplex.html)

The full celebration takes place on the day of the feast. The vigil anticipates and prepares for the feast by means of fasting and self-denial, signified by the violet color of the Mass vestments.

Another element of modern corruption of Hallowe’en which is a contradiction: the glut of candy. Not a healthy celebration at all. For body or spirit.

From the Martyrology {anticip.} for this day:

The morrow is the Feast of All the Saints. This famous feast was instituted to be held every year throughout the whole city of Rome, in honour of the Blessed Virgin Mary, Mother of God, and of all the holy martyrs, by Pope Boniface IV, after he had consecrated to Christian worship the temple called the Pantheon or Temple of all the gods. And the same festival was afterwards being kept in diverse ways in diverse churches, when Gregory IV decreed that it should be solemnly observed for ever throughout the universal Church upon the first day of November, in honour of all the Saints.