Turns out, Halloween has been with us for a long time! It started as an ancient, pre-Christian, Celtic festival of the dead. Back then, for the Celts, November 1 was their New Years and it was the day they switched from autumn to winter. It was also the time of year that they believed the veil between the world of the living and the world of the dead was at its thinnest. That meant that the dead could hang out with the living. That’s not comfortable for anybody! They had a festival called Samhain (pronounced Sow-en) and it was the most significant holiday of their entire year. They believed that it was on Samhain that the souls of people who had died during that year finally traveled to the otherworld. To help them get there, the living people lit bonfires to honor the dead, to help them along their journey, and also to keep them away from the living.
In the early centuries of the first millennium, Christian missionaries showed up and they wanted to change the religious practices of the Celts. But, rather than destroying the existing pagan holidays, such as Samhain, they tried to transform it. What the missionaries did was basically say, “Hey all those supernatural deities you worship? They’re evil, they’re demonic, and they’re scary.” Then they put the new Christian holiday on November 1, All Saints Day. So now, everyone was supposed to worship the saints on November 1, instead of the dead, during the festival of Samhain. It didn’t work. All Saints Day became known as All Hallows and it was the night before All Hallows, the eve of All Hallows, that people continued to celebrate in the spirit of Samhain as a time of the wandering dead.
Eventually, All Hallows Eve became Hallow Evening, which eventually became Halloween. Basically an ancient, Celtic, pre-Christian new year celebration lost its pagan context over the last couple thousand years and transformed into one of the largest secular holidays of modern times.