I do not intend any disrespect to the cleric who wrote this essay, but there are a number of errors or assertions that lack any real support in it.
These pagan peoples believed that physical life was born from death.
Since the early Celts and Britons did not leave much in the way of written records, I wonder what source is used for this.
A certain deity, whom they called Samhain, was believed by the Celts to be the lord of Death, and it was he whom they honored at their New Year's festival.
This is an often repeated idea that is just not true. There is NO Celtic god of death named "Samhain"/"Samain"/etc which by the way is pronounced more like "Sow'en". It is the gaelic word that means "Summer's End".
Here is a Christian site with information on Halloween. Along with looking at pagan and Christian customs in history, near the bottom of the first page is some information about just *when* "Trick or treat" started. It isn't "druidic" by many many centuries. The earliest written record of it that the author found is from 1938.
http://www.new-life.net/halowen1.htmhttp://www.new-life.net/halowen2.htmHere is a site from Ireland about it
http://www.irelandforvisitors.com/articles/samhain.htmAnd as a side note, there is not much record at all of just what the Druids or any other Celtic religions did or believed. I will again recommend "The Pagan Religions of the Ancient British Isles" by Ronald Hutton, a scholar at the University of Bristol in England. Another of his books that I found good is "Stations of the Sun: a History of the Ritual Year in Britain" which is about the folk customs of the year and how they go along with Christianity.
If desired, I can also provide neo-pagan sites that also say that there is no such spirit/god as "Samhain". This got started somehow, I suspect by someone who didn't understand what they were reading or didn't comprehend other cultures and then it got picked up by others and it took off.
On the eve of the New Year's festival, the Druids who were the priests of the Celtic cult, instructed their people to extinguish all hearth fires and lights. On the evening of the festival a huge bonfire built of oak branches, which they believed to be sacred, was ignited. Upon this fire sacrifices of crops, animals, and even human beings, were burned as an offering in order to appease and cajole Samhain, the lord of Death.
Again, I wonder what the source is for this, the extinguishing of the lights in particular. There is the instance of St. Patrick in Ireland kindling a fire when no one was supposed to until that of the High King at Tara was lighted. But in that case the saint was lighting the Pascal fire, that is to say, it was in the Spring. But whatever the case there would not have been a fire to any "Samhain" (see above).
The dialogue of "trick or treat" is also an integral part of this system of beliefs and practices. It was believed that the souls of the dead who had entered into the world of darkness, decay, and death, and therefore into total communion with and submission to Samhain the lord of Death, bore the affliction of great hunger on their festal visit. Out of this grew the practice of begging, which was a further ritual enactment and imitation of what the Celts believed to be the activities of the souls of the dead on their festal visit. Associated with this is the still further implication that if the souls of the dead and their imitators were not appeased with "treats," i.e., offerings, then the wrath and anger of Samhain, whose angels and servants the souls and their imitators had become, would be unleashed through a system of "tricks," or curses.
This reads like some of the "Jack Chick" booklet that the pastor refers to on the site I've linked to. "Begging" in the sense of going about and getting something is a British Isles custom at such times as Christmas (wassailing the neighbors for example, or the "Wren Boys" on St. Stephen's Day) and, I've been told, to get things to mark "Guy Fawkes Day" on the 5th of November ("Remember, remember, the Fifth of November/Gunpowder, Treason and Plot...")
http://www.hymnsandcarolsofchristmas.com/Hymns_and_Carols/Notes_On_Carols/wassailing.htmhttp://www.irishfestivals.net/saintstephensday.htmAs a side note, in Japan the Feast of O-bon in the summer, marks the belief that one's ancestors return for a visit. It's a festival to remember those who have passed on. And on November 1 is, of course Dia de Muertos with candy skulls and customs to set out food that family members liked. It is a Human thing to want to remember our family and friends who have passed away. But I suspect that someone who did not know about the culture and customs of Japan or Mexico might just to a conclusion that it was "satanic"
I will also confess that I'm having a bit of a difficulty with this sentence:
For if we participate in the ritual activity of imitating the dead by dressing up in their attire or by wandering about in the dark, or by begging with them, then we have willfully sought fellowship with the dead, whose lord is not Samhain as the Celts believed but Satan, the Evil One who stands against God.
The "lord" of the dead is Satan? Ummm, I thought that God was the lord of those who have gone before us. Perhaps I'm not fully understanding his ideas.
Further, if we submit to the dialogue of "trick or treat," we make our offering not to innocent children, but rather to Samhain, the lord of Death whom they have come to serve as imitators of the dead, wandering in the dark of night.
I'm sorry, no such being, and when I hand out Hershey's and Smarties it's to the 10 y.o. at the end of the block dressed as a princess and the boys in the football uniforms (and then there are our kids who've been such things as a rocket ship, "Arthur and DW" (type casting it was) Legolas and a "little Hobbit Girl", Raggedy Ann (Important note: after colouring the string mop head in the Rit red dye, do NOT put it in the dryer.. Do NOT. You'll get a mess of fibers and strings and have to start all over again.) an elephant, a dinosaur, and ear of corn, a Blue Crab (we were insane that year), Faramir, and more. Not a gruesome thing in the lot.
Out of this arose the practice of the jack o'lantern (in the USA, a pumpkin; in older days other vegetables were used) which was carved in imitation of the dead and used to convey the new light and fire to the home where the lantern was left burning throughout the night. Even the use and display of the jack o'lantern involves celebration of and participation in the pagan festival of death honoring the Celtic god Samhain.
No, this is not the case. What we now know as the Jack O'lantern comes from a folktale involving a man named Jack. Here is one version and an interesting letter about the custom:
http://www.new-life.net/halowen4.htmhttp://www.new-life.net/halowen7.htm#turnipIn the days of the early Celtic Church, which was strictly Orthodox,
Again, I mean no disrespect, but I wonder what he means by that and what his sources are for much of the rest of the essay.
The Western Church's attempt to supplant this pagan festival with the Feast of All Saints failed.

It's a Principal Feast and supplants regular Sunday liturgies if November 1 should fall on that day of the week and if it falls during the week it is moved to the next Sunday. It is never missed.
That was a simple renaming of a very old satanic feast of Walpurgis Night (night of April 30 into the day of May 1) - the great yearly demonic Sabbath during which all the participants united in "a fellowship of Satan."
Just as a side note, Walpurgis is the feast day of St. Walburga, an abbess and missionary to the Germanic people in the 700's. The pagan name for the start of summer is "Beltain" and it is marked by lighting fires. (Considering that for most of human history the only way to have light in darkness was fire it's not surprising that bonfires or lanterns or other lights are part of celebrations and rituals. One may recall that William Manchester wrote a book called "A World Lit Only by Fire"). From my reading that is the holiday that St. Patrick lit his fire before the High King's.
If anyone would like more links and titles, I will be glad to provide them. .... Or I may have gone far enough that people's eyes are glazing over.

Ebor