What does Santa Claus and decorating trees have to do with Biblical Christianity?
What is Christmas really about?
Santa Claus, gift-giving, mistletoe, decorating trees, yule logs, and most other Christmas traditions have absolutely no basis in the Bible whatsoever. The Bible does not even instruct us to celebrate the birth of Yahshua the Messiah (aka 'Jesus'), much less tell us that his birthday was December 25th. So what are the real origins of this "holy day"?
The holiday known as 'Christmas' originates from pagan winter solstice celebrations, and was "Christianized" by the Roman Catholic Church. And there is a much darker side to "Santa" and Christmas than may appear at the surface.
Ancient Babylonian and Roman Winter Solstice Celebrations
In ancient Babylon, the feast of the Son of Isis (Goddess of Nature) was celebrated on December 25. Raucous partying, gluttonous eating and drinking, and gift-giving were traditions of this feast. In ancient Rome, a winter festival called 'Saturnalia' was celebrated from December 17th to December 23rd in honor of their god Saturn. It was a once-a-year time to indulge in feasting, drinking, the exchanging of gifts, and merrymaking in general.
The pagan peoples of northern Europe also celebrated the winter solstice in a holiday known as 'Yule', in which they honored their pagan gods and celebrated "for a fertile and peaceful season", including fertility sacrifices. Trees and other greenery decorated the inside of homes in order to remind people of the soon return of Spring. It was customary to light a candle to encourage the sun god--and the sun--to reappear the following year.
The traditions from Yule heavily influence Christmas, including the use of greenery indoors, the Yule log, and kissing under mistletoe.
The Yule log was the center of the trunk of a tree that was dragged to a large fireplace where it was supposed to burn for twelve days. From this comes the twelve days of Christmas.
The source of "kissing under the mistletoe" is pagan Celtic-Norse rituals and mythology.
Mistletoe was considered by the pagan Druids to be a 'sacred' plant having medicinal qualities and mysterious supernatural powers, especially helping fertility. The custom of kissing under the mistletoe began as a fertility ritual. 
Mistletoe was also used by the pagan Romans in fertility rites.
Decoration of Trees and use of Greenery Indoors
The decoration of homes with greenery during the dead of winter was done as a reminder that the warmer spring and summer months would soon eventually come.
At the winter solstice, the Romans decorated their homes with evergreen trees and boughs of laurel. The pagan Northern Europeans used holly, ivy and bay for both decoration and in their religious rites at their solstice observance. Hollyberries were believed to be a "food of the gods." In northern Europe, evergreen branches were used as means to "ward off evil spirits." The use of the Christmas tree also goes back to the early Druidic practice of tree worship.
In Rome, Saturnalia was celebrated by groups of people singing in the streets. This is the origin of 'carrolling'.
Many people associate gift-giving with the wise men and their presents to the young 'Jesus', but this practice is also of pagan origin. The Romans exchanged "good luck" presents during Saturnalia, in which the wealthy gave gifts to the poor in honor of the "golden age of liberty when the god Saturn ruled the known world". 
Church of Rome renames Saturnalia festival "Christ's Mass"
Saturnalia was popular among the pagan Romans in the early years of the Roman Catholic Church following when Constantine decreed his version of 'Christianity' as the official religion of Rome. In order to make it easier for the pagans to convert to Christianity as well as further paganize and corrupt the true Israelite religion, the Romish Church simply encouraged the continued observance of Saturnalia, but ascribed 'Christian' meanings to the pagan rituals, and gave the festival the name "the Mass of Christ" or "Christ's Mass." Instead of the birth of the Sun god, this was now the 'birth of Christ.'
Puritans Rejected 'Christmas' - 'Holiday' suppressed from 16th to 19th Centuries
The Puritans, citing its pagan origins, believed Christmas should not be observed. Prominent Puritan William Prynne, during the time of king Charles I, wrote:
"Our Christmas lords of Misrule, together with dancing, masques, mummeries, stage-players, and such other Christmas disorders, now in use with Christians, were derived from these Roman Saturnalia and Bacchanalian festivals; which should cause all pious Christians eternally to abominate them" (The Book of Christmas Folklore, p. 8).
The observance of Christmas was made illegal in Scotland in the 16th century. It was also made illegal in many parts of the United States in the early days of the nation, mainly in New England states such as Massachusetts where the Puritan influence was strong.
Due to the influence of the Puritans in Britain and the United States, celebration of Christmas was suppressed in the Anglo-Saxon world from the 16th through the 19th century. Over the last century, due mainly to mass media influence, Christmas observance has exploded in popularity.
Yahshua the Messiah actually born in the Fall
The Bible provides evidence which shows that December 25 is the incorrect date for Yahshua the Messiah's birth. From the biblical description, his birth actually occurred in the Fall, most likely September.
It is very unlikely that He was born in December, since the Bible records shepherds tending their sheep in the fields on that night. In Luke 2:8 it is written: "And there were in the same country shepherds abiding in the field, keeping watch over their flock by night."
YHWH commands "Learn not the way of the heathen."
In the Bible, YHWH sternly warns his people time and time again to have nothing to do with paganism, which is idolatry and worship of false gods.
The prophet Jeremiah instructed the Israelites to not cut down trees and adorn them as the heathens:
"Thus saith the Lord, Learn not the way of the heathen, and be not dismayed at the signs of heaven; for the heathen are dismayed at them. For the customs of the people are vain: for one cutteth a tree out of the forest, the work of the hands of the workman, with the ax. They deck it with silver and with gold; they fasten it with nails and with hammers, that it move not." (Jeremiah 10:2-4)
Who is really celebrated at winter solstice observances?
The ancient pagan winter solstice festivals were part of the worship of the sun and their gods - Tammuz in Babylon, Horus in Egypt, Saturn in Rome, and Mithras in Persia and Rome. These gods have been identified by experts in the occult as associated with Satan.
Santa or Satan?
The name 'Santa' is an anagram for 'Satan'. The rearranging of letters (called anagrams) to hide secret names or words has long been practiced in the occult.
Satan seeks to imitate the most high YHWH and be worshipped like him. Consider the fact that 'Santa' is dressed in red (Revelation 19:13, "And he was clothed with a vesture dipped in blood: and his name is called The Word of God"), has white hair and a beard (Revelation 1:14, "His head and hair were white like wool, as white as snow"), is omniscient (ie, "knows whether children have been good or bad"), omnipresent (can travel the whole world over in one night), rides the heavens with the help of magical beasts, resides in the North (Isaiah 14:13, "For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north"), "brings good gifts", is a carpenter, and asks children to pray to him. "St Nick" is another name for Santa Claus, while "Old Nick" is an epithet-nickname for Satan. In medieval plays, the trademark line or laugh for Satan, or the devil, was "Ho ho ho". 
Is all of this just a coincidence? Or something more sinister?
The early years of a child's development are crucial (eg, Proverbs 22:6: "Train up a child in the way he should go: and when he is old, he will not depart from it."). Jesus also said “Truly I tell you, unless you change and become like little children, you will never enter the kingdom of heaven." (Matthew 18:3)
Not only are children hoodwinked into pagan and materialistic practices at Christmas, but are further injured by being lied to about a "Santa" that they are later told is fictionial and does not exist. Consider what harm this does to childrens' "childlike faith" and ability to believe their parents about the existence of 'God'.
Elves, "Santa's little helpers"
What is the significance of elves, who are known as supernatural beings "with magical powers who exercise a mischievous interference in human affairs"?
Occult researchers and authors describe elves as "demonic entities" associated with witchcraft and sorcery. In "The Encyclopedia of Witches and Witchcraft", Rosemary Ellen Guiley says of Elves:
"A host of supernatural beings and spirits who exist between earth and heaven. Fairies or Elves are fallen angels. When God cast Lucifer from heaven, the angels who were loyal to Lucifer plunged down with him." (The Encyclopedia of Witches and Witchcraft, p. 115) 
"And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him" - Revelation 12:9
The 'traditions of men' or the word of YHWH?
Apologists who do not know the true YHWH and his laws will say that even if Christmas has pagan roots it is still "acceptable" to celebrate it because it is "done with good intentions" and attempting to "honor Jesus."
On the surface, it may appear 'good' and harmless. But underneath, it rooted in darkness -- ie, the worship of false gods and nature, friviolity, materialism, gluttony, and debauchery.
And then to take the holy name of YHWH and Yahshua and profane them by using them in association with such vile pagan practices. That is truly an abomination.
In every age, people must decide whether they just "go along with the crowd" on the easy, wide road that leads to destruction -- or whether they will follow the narrow way, taking the words and commandments of YHWH seriously, unto their salvation and eternal life.