Keep in mind that there is a LOT of competing information out there about the history of Christmas. I have worked to find the truth, but my presentation is only as good as my sources, which I hope were reliable.
- Origen(185-254) said it would be wrong to honor Christ in the same way Pharaoh and Herod were honored. Birthdays were for pagan gods.
- Tertullian (155-240), among others, did not list Christmas as a Christian celebration.
- Irenaeus (130–200) mocked Roman celebrations of birth anniversaries, dismissing them as “pagan” practices—a strong indication that Jesus’ birth was not marked with festivities at that place and time.
Romans observed Saturnalia between December 17-25 (I have seen different end dates, but this date is the most commonly cited). It was a holiday in honor of Saturn, “the birthday of the unconquered sun,” and it was a party (to say the least) characterized by a lot of personal and societal chaos. 
In the 300s, Pope Julius I chose December 25 as a time to celebrate the birth of Jesus, perhaps to accommodate converts who were used to being a part of the Saturnalia festival. There was plenty of imagery to tap into (light over darkness, conquering the Lord of Misrule, the birth of the unconquered ‘son’, etc).  This trend caught on.
- Jesus’ birthday is listed as December 25 in a mid-fourth-century Roman almanac that lists the death dates of various Christian bishops and martyrs. The first date listed, December 25, is marked: natus Christus in Betleem Judeae: “Christ was born in Bethlehem of Judea. A Christian writer in 320 noted: “We hold this day holy, not like the pagans because of the birth of the sun, but because of him who made it.”
- By AD 386, Chrysostom was preaching, "Without the birth of Christ there is no Baptism, no Passion, no Resurrection, no Ascension and no Pouring out of the Holy Spirit..."
- No longer was the celebration of the birthday of Jesus a thing to dismiss as a meaningless pagan practice. Just....be temperate.
- In 389 St Gregory (one of the Four Fathers of the Greek Church) warned against 'feasting in excess, dancing and crowning the doors'. 
- Augustine (354-430 AD) wrote: “So then, let us celebrate the birthday of the Lord with all due festive gatherings.”
During the Middle Ages (400-1400) Christianity eventually became a formative force behind this celebratory time. While the church formally increased the focus, a lot of the informal celebration was not as focused. The poor would go to the rich and demand their best food and drink, like a Christmas version of trick or treat. There was a significant economic 'Reason For The Season' as Christmas became a time when the rich at least made a gesture at leveling the unfair economic score by entertaining the poor.
The earthly benefits remained a focal point for a long time. The Church began a Midnight Mass on Christmas Eve (“Christ’s Mass” 1039); one reason this was such a celebration was that it marked the transition from fasting to feasting. As much as the Church formally focused on Jesus, Christmas was never fully able to avoid excess once it got outside the confines of the church building.
In the 1640s, Puritan Separatists who ‘separated’ from the Church of England sailed across the pond and came to America, with no desire to continue the observation of Christmas. (Christmas was a time of drunkenness, rioting and “misrule’, unfortunately).
When Oliver Cromwell and the Long Parliament took over England around that same time (1645), they vowed to rid England of decadence and, among other things, cancelled all Christian holidays except Sunday. They even changed the name of Christmas to “Christ-tide” to avoid the word “mass.”
Charles II resurrected the holiday when he was restored to the throne in 1660, and it has remained ever since.
The Puritans did NOT bring Christmas with them to what we now call the New England states. In fact, from 1659 to 1681, the celebration of Christmas was outlawed in Boston (you could be fined five shillings for exhibiting Christmas spirit). If we want to talk about the War on Christmas in the history of U.S. culture, the Puritans win hands down.
On the other hand, John Smith reported that Christmas was enjoyed by all at Jamestown, which was settled by Anglicans, people who still were loyal to the Church of England.
Fast forward to the 1800s. Unemployment and poverty were high, and actual riots by the poor often occurred during Christmas. A policeman was actually killed trying to stop a fight between Catholics holding a Christmas Mass and Protestant fundamentalists trying to stop them.“Christmas joined Sabbath observance, slavery, women’s rights, corruption, immorality, crime, drugs, prostitution, gambling and alcohol, as major moral issues that risked plunging the city and the nation into chaos during the early decades of the young republic. In fact, daily violence reached such proportions that in 1828 the city established its first professional police force following an especially violent Christmas riot. “
In 1819, Washington Irving wrote a book (The Sketchbook of Geoffrey Crayon, Gent) that was basically a series of stories/essays that featured an English squire who invited the peasants into his home for the holiday where the two groups mingled in friendship. To Irving, Christmas should be a peaceful, warm-hearted holiday that united people from every walk of life. He also wrote "Diederich Knickerbocker's History of New York," in which Sinterklaes rode through the skies in a horse and wagon and went down chimneys to deliver presents to children.
Around that time, Charles Dickens wrote A Christmas Carol, a novel which had a huge impact in both England the U.S. Note, once again, a strong economic 'Reason for the Season' in both these influential books as opposed to a spiritual reason for observing Christmas.
This is when people in the United States really began to see Christmas as a national holiday characterized by love, generosity and warmth. The U.S. being the melting pot that it was, people began building traditions from all sorts of sources,  Still, as late as 1855, Presbyterians, Baptists and Methodists did not celebrate Christmas, while Episcopalian, Catholic and German churches did. Southern Baptists started moving in that direction after the Civil War ended in the 1860s.
In June 26, 1870, Christmas was officially declared a federal holiday (a number of states, especially from the Anglican tradition in the South, had already made it a state holiday).
To summarize: the Church embraced a cultural holiday and sought to redeem it. I have no problem with this; in fact, I think it’s a great idea. At the same time, we must be honest that we moved into an existing celebration, and the cultural observance has always had a strong influence. These two focuses have always lived in tension, with an ebb and flow to which focus moves front and center. More on this later.
THE CHRISTMAS TREE: Pagans had long used trees as an accompaniment to their worship (the oak was a popular one). Christianity did not ban trees; it changed the focus. The first documented Christmas trees came from Christians in 1441 in Estonia and in 1510 in Latvia. According to Marcia Montenegro, the tree represents the wood that turns bitter to sweet, condemnation to redemption. Around 700, the fir tree became popular as a symbol of Christianity (because of its triangle shape /the Trinity). The ‘ever green’ was also associated with eternal life.
TINSEL: Legend says a poor family wished to decorate their Christmas tree but had nothing. A spider spun a web on the tree at night, and Baby Jesus turned those threads into silver.
CANDY CANE: the shepherd’s crook of the Good Shepherd.
POINSEETTIAS: the star of Bethlehem.
WREATH: a symbol of true love, which never ceases.
HOLLY: a symbol of the crown of thorns worn by Christ on the cross.
BELLS: Bells stand for joy, and as a reminder that Jesus is the Great High Priest (Jewish priests had bells attached to the hem of their robes).
TREE BAUBLES OR BALLS: In early church calendars of saints, December 24th was Adam and Eve's day. The tree became a symbol of the tree of Paradise, and people started decorating it with red apples (originally the apples were a reminder of sin; they morphed into a symbol for the fruits of the Spirit).
LIGHTS: Around 1500, Martin Luther brought a tree indoors and decorated it with candles in honor of Christ’s birth (indoor stars!). 
MISTLETOE (“dung twig”): The Druids associated it with fertility. In the Middle Ages in England, it was hung to ward off evil spirits and witches. In Scandinavia, it was a plant of peace. In Norse legend, it was a symbol that reminded them to protect life. In many cultures it was considered a cure-all medicine. The Catholic church banned it for a while because of how much the pagans loved it, but it’s easy to see how it blended into a celebration of a baby that would heal all nations and bring peace, and who died so we could live.
CHRISTMAS PRESENTS: a reminder of the gifts of the Magi, and of God’s gift of Jesus to us.
SAINT NICHOLAS/SANTA CLAUS: The Catholic Church associated gift giving with Saint Nicholas, one of the bishops who convened the Council of Nicaea in 325. Legend says he became aware of some desperate needs in his congregation (a desperate family selling their children into slavery, among other things), so he gave money, fruit, food, etc.
In 1809, Washington Irving (remember him?) wrote a story that featured a white bearded, flying-horse riding Saint Nicholas using his Dutch name, Santa Claus.
Then, in 1822, we got this iconic poem (based on Irving’s writing): “Twas the night before Christmas, when all through the house, not a creature was stirring, not even a mouse. The stockings were hung by the chimney with care, in the hope that Saint Nicholas soon would be there…”
In 1931, the Coca Cola insisted that Santa, who was the face of their new campaign, be in a bright, Coca Cola red suit.
So, who is Santa Claus? A Christian bishop from the Council of Nicaea filtered through Celtic gods, Dutch culture and American cartoons, and brought to you by Coca-Cola.
1. I’m not bothered by the pagan history of Christmas (and if you think Christians originated the holiday rather than borrowing it, cool. Carry on). Christianity has a rich tradition of moving into cultural celebrations or images and redeeming them to point to toward Jesus. Art, music, symbols and holidays have been subverted and converted to the glory of God for 2,000 years.
If Starbucks wants to print a cup that says “Happy Saturnalia,” and businesses require employees to say “Happy Holidays,” that’s their call. They don’t worship like I do. Meanwhile, Hobby Lobby and Chick-Fil-A will say Merry Christmas. Cool. So will I. The church has always lived in this tension. Our job is to be Christ-like in the midst of it.
 He received a tradition that the Roman emperor Augustus reigned 43 years and was followed by the emperor Tiberius. Jesus was 30 in the 15th year of Tiberius’ reign (Luke 3), which meant he lived 15 years under Augustus (so, born in the 28th year of Augustus reign).
 An anonymous document from North Africa placed Jesus birth on March 28; Clement (bishop of Alexandria) thought Jesus was born on November 18. Based on historical records, another dude (Fitzmyer) guessed that Jesus was born on September 11, BC 3.
 Some of the upper classes celebrated the birthday of Mithra, the god of the unconquerable sun who was born of a rock, on December 25.
 The Greek writer Lucian said there were other customs as well, like going from house to house while singing naked consuming human-shaped biscuits.
 “In an old list of Roman bishops, compiled in A. D. 354 these words appear for A.D. 336: "25 Dec.: natus Christus in Betleem Judeae." December 25th, Christ born in Bethlehem, Judea. This day, December 25, 336, is the first recorded celebration of Christmas.” https://www.christianity.com/church/church-history/timeline/301-600/the-1st-recorded-celebration-of-christmas-11629658.html
 For example, German immigrants brought their tradition of putting lights, sweets and toys on the branches of evergreen trees placed in their homes.
 As for nativity scenes…the Gospels do not mention there being any oxen, donkeys, camels or Magi at the manger. The Gospel of Pseudo-Matthew, a medieval text, has heavily influenced the images in our heads as well as our Christmas songs.
Tradition about the Magi built from some assumptions from OT passages (Isaiah 1:2-3; 60:3, 6, 10-11;Psalm 72:10). An early church leader named Origen decided that Genesis 22 had something to say about the Magi, so he set the number at 3. Don’t ask me to explain why.
 A story is told that, one night before Christmas, he was walking through the forest and looked up to see the stars shining through the tree branches. It was so beautiful, that he went home and told his children that it reminded him of Jesus, who left the stars of heaven to come to earth at Christmas.
 A satire of Dutch culture called Knickerbocker History.