The reason that we celebrate the holiday season is because it is the birthday of Jesus Christ. Although the holiday has come to mean a lot more to a lot of people, the birth of Jesus is the biggest reason that the holiday season exists. Most people at least acknowledge his role in the holiday.
Jesus is the answer for the world today. Among him there's no other Jesus is the way. Mountains bow down and the seas will roar at the sound of your name. I sing for joy at the works of your hands. Forever I'll love you forever I'll stand. Nothing compares to the promise i have in you
You can't really deny that Christmas is a celebration of Jesus's birthday. That's how it started, and that's why Christmas exists. A lot of people might not think of Jesus anymore, but he is the reason for the season. He is the reason for a lot of Christmas traditions, and the holidays would hardly exist today without him.
The event Christmas comes from Christ himself. Though there may be pagan events on this day, according to the other side, it is not Christmas. Only Jesus is the reason for Christmas. Without Jesus, there will no be such thing as Christmas. No matter holidays exist before Christmas, it is impossible to name a holiday "Christmas" if there is no Christ.
The Pope decided to make the popular pagan midwinter/solstice festivals the date the Catholic (at which time was the only Christian) Church would celebrate the birth of their savior figure, since it was so many other savior figures' birthday, and it was easier to convert people by allowing them to keep their traditions, as long as they were continued in a Christian context.
Historically speaking, Pagans and other nature-based faiths in the Northern Hemisphere celebrated the winter solstice as a return of their Sun God(s), since this is when the daylight hours start getting longer again. When Christianity came along these festivals and celebrations were incorporated into Christianity in order to gain followers. This was also a time when the Bible wasn't easily read, as common folk typically couldn't read or write and books weren't exactly commonplace due to the methods of scribing. If you research a number of polytheistic religions will contain very similar stories to those included in the Bible, such as a divine birth, resurrection, etc. And if we're looking at the more commercial aspect of Christmas, well we can look at Odin as Santa Clause, since they have striking similarities.
This is an economic and civic holiday, and it has been since just post-WWII. The holiday's origins are rooted in paganism, but that shifted to Christianity. However, both of those factors have been dwarfed by regular old consumerism. Spending accounts for 70% of US GDP, and over half of that spending occurs in the months of December and January. So, pray for spending this year, or you might get stuck in a manger next year, with nothing but the sun to warm your chilled body.
Most European peoples celebrated midwinter holidays long before the development of Christianity. With the spread of Christianity, Christian elements were mixed with these ancient celebrations. Because of this, most of our modern Christmas traditions originate in the pre-Christian, primarily Roman and Germanic 'pagan' observances. Thus Jesus is really not the 'reason for the season', but rather a later addition to a very ancient midwinter European holiday.
Christmas the way that we celebrate it traditionally, is actually of pagan origin(even the X-mas tree) which only over time has been adapted as a Christian holiday of Jesus's birth. Jesus by all known historical context was born not on December 25 as many would believe but actually in early March. December 25 is actually a holiday commemorating the sun god by early pagans, as the 25th is the first day after the winter solstice that the days begin to get longer. We celebrate this day as Jesus's birth though because it was such as deeply rooted holiday in the early European culture between 500 and 1200 A.D that instead of making the mandated holiday change from December 25 to sometime in early spring the church just changed the date of Jesus's birth to fit current celebrations which also helped convert many to early Christianity. And that is how Christmas was born.