Halloween is one of many modern observances that we have inherited from our fathers, yet is not rooted in scripture. For me, the fact that it is not rooted in scripture is all the evidence I need to not observe it. But I do recognize the value in looking at the history of the 'un-holi-day' and seeing if it is rooted in idolatry.

A little History.

According to various Encyclopedia's, the origins of this holiday are of demonic origin. Listed below are some quotes. 

Encyclopedia.com's Electric Library: 

Halloween.
Pronounced As: halwn, häl- , Oct. 31, the eve of All Saints' Day, observed with traditional games and customs. The word comes from medieval England's All Hallows' eve (Old Eng. hallow="saint). However, many of these customs predate Christianity, going back instead to Celtic practices associated with Nov. 1-the beginning of winter and the Celtic new year. Witches and other evil spirits were believed to roam the earth on this evening, playing tricks on human beings to mark the season of diminishing sunlight. Bonfires were lit, offerings were made of dainty foods and sweets, and people would disguise themselves as one of the roaming spirits, to avoid demonic persecution. Survivals of these early practices can be found in countries of Celtic influence today, such as the United States where children go from door to door in scary costumes demanding "trick or treat.

Encyclopedia Britannica:

Halloween, also called All Hallows' Eve or All Hallows' Evening, a holy or hallowed evening observed on October 31, the eve of All Saints' Day. In modern times, it is the occasion for pranks and for children requesting treats or threatening tricks. In ancient Britain and Ireland, the Celtic festival of Samhain eve was observed on October 31, at the end of summer. This date was also the eve of the New Year in both Celtic and Anglo-Saxon times and was the occasion for one of the ancient fire festivals when huge bonfires were set on hilltops to frighten away evil spirits. The date was connected with the return of herds from pasture, and laws and land tenures were renewed. The souls of the dead were supposed to revisit their homes on this day, and the autumnal festival acquired sinister significance, with ghosts, witches, hobgoblins, black cats, fairies, and demons of all kinds said to be roaming about. It was the time to placate the supernatural powers controlling the processes of nature. In addition, Halloween was thought to be the most favorable time for divinations concerning marriage, luck, health, and death. It was the only day on which the help of the devil was invoked for such purposes.

Encarta Encyclopedia:

Origins, Halloween: Many of the ancient peoples of Europe marked the end of the harvest season and the beginning of winter by celebrating a holiday in late autumn. The most important of these holidays to influence later Halloween customs was Samhain, a holiday observed by the ancient Celts, a tribal people who inhabited most of Western and Central Europe in the first millennium BC. Among the Celts, Samhain marked the end of one year and the beginning of the next. It was one of four Celtic holidays linked to important transitions in the annual cycle of seasons.
Samhain began at sundown on October 31 and extended into the following day. According to the Celtic pagan religion, known as Druidism, the spirits of those who had died in the preceding year roamed the earth on Samhain evening. The Celts sought to ward off these spirits with offerings of food and drink. The Celts also built bonfires at sacred hilltop sites and performed rituals, often involving human and animal sacrifices, to honor Druid deities.

Does this sound like something we ought to be imitating? Do we really want our children dressing up like witches and demons roaming about the streets and demanding offerings from human beings? And worse yet, threaten to bring some unwanted harm on the person if they refuse to give the child (imitating demons) an offering in the form of a treat? The obvious answer to the above questions for any believer in Yahweh is no! 

What does Scripture say?

Let's look at what scripture says about witches: 

Exodus 22:18 Thou shalt not suffer a witch to live.

Deuteronomy 18:10 There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch, 11 Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer.
12 For all that do these things are an abomination unto Yahweh: and because of these abominations Yahweh thy Elohim doth drive them out from before thee.

Galatians 5:19 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, 20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, 21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of Elohim.

So are our we and our children supposed to imitate witches and demonic practices or are we supposed to imitate Yahushua the Messiah?

We read later that Christians took the observance and "Christianized" it. Continuing the MS Encarta Encyclopedia article above: 

Origins, Halloween: By the end of the 1st century AD, the Roman Empire had conquered most of the Celtic lands (see Rome, History of). In the process of incorporating the Celts into their empire, the Romans adapted and absorbed some Celtic traditions as part of their own pagan and Catholic religious observances. In Britain, Romans blended local Samhain customs with their own pagan harvest festival honoring Pomona, goddess of fruit trees. Some scholars have suggested that the game of bobbing for apples derives from this Roman association of the holiday with fruit.
Pure Celtic influences lingered longer on the western fringes of Europe, especially in areas that were never brought firmly under Roman control, such as Ireland, Scotland, and the Brittany region of northwestern France. In these areas, Samhain was abandoned only when the local people converted to Christianity during the early Middle Ages, a period that lasted from the 5th to the 15th century. The Roman Catholic Church often incorporated modified versions of older religious traditions in order to win converts. For example, Pope Gregory IV sought to replace Samhain with All Saints' Day in 835. All Souls' Day, closer in spirit to Samhain and modern Halloween, was first instituted at a French monastery in 998 and quickly spread throughout Europe. Folk observances linked to these Christian holidays, including Halloween, thus preserved many of the ancient Celtic customs associated with Samhain.

So we see that the roots of this festival are found to be in demonic idolatry. Some Christians tried to "Christianize" it to appease the idolaters, but who really converted who in this situation? It seems to me that it was the idolaters that converted the Christians! Believers are supposed to set the standard, not imitate the world and have a "Christian" version of everything like we see is so common today.

Does it Matter?

Does Yahweh say that it is alright to observe the pagan festivals as long as we are honoring Him? Notice carefully what he said to the Israelites before they entered the promised land.

Deuteronomy 12:29 (KJV) When Yahweh thy Elohim shall cut off the nations from before thee, where thou goest to possess them, and thou succeedest them, and dwellest in their land; 30 Take heed to thyself that thou be not snared by following them, after that they are destroyed from before thee; and that thou enquire not after their gods, saying, How did these nations serve their gods? even so will I do likewise. 31 Thou shalt not do so to Yahweh thy Elohim: for every abomination to Yahweh, which he hateth, have they done to their gods; for even their sons and their daughters they have burnt in the fire to their gods. 32 Whatever thing I command you, observe to do it: thou shalt not add to it, nor diminish from it.

What we are really looking at here is Satanism's influence today:

"After one's own birthday, the two major Satanic holidays are Walpurgisnacht (May 1st) and Halloween (or All Hallow's Eve)." The Satanic Bible by Anton Levey page 96, section on Religious Holidays.

But Scripture says: 

1 Corinthians 10:21 Ye cannot drink the cup of Yahweh, and the cup of devils: ye cannot be partakers of Yahweh's table, and of the table of devils.

Let's stop the mixing of cups and the partaking of two tables. Let's instead turn unto Yahweh. Clearly, very clearly, it does matter!

 https://www.eliyah.com/hallween.html