Well, two big reasons show up in history.
One reason is a theological calculation that shows up early. A Christian writer named Sextus Julius Africanus (early 200s) argued that Jesus was conceived on March 25 and was born nine months later on December 25.
Another reason is the Roman winter season. By late December, the empire already had major celebrations, including solstice-related festivals such as the celebration of Sol Invictus on December 25. Some historians think placing Christmas then helped the church speak into a season people already treated as special.
By the 300s, December 25 had become the dominant date in the Western church, with firm evidence that Rome was celebrating the Nativity on that date by the mid-300s.
Christmas Eve, Why December 25, and Did It Happen That Day
Christmas Eve has a certain feeling to it.
Even if the house is noisy, even if the schedule is packed, there is still a sense that we are standing on the edge of something. For many families, December 24 is when the last candle gets lit, the last dish gets made, and the last person finally walks through the door.
So today, I want to do something a little different.
Instead of going to one country, I want to talk about one question that comes up every year.
Was Jesus actually born on December 25? If we do not know that for sure, why do we celebrate Christmas on December 25 anyway?
This is one of those questions where people often hear a quick answer, then repeat it for years. The real story is more interesting and more honest.
What the Bible tells us, and what it does not
The first thing to say is simple.
The New Testament does not give a calendar date for Jesus’ birth.
It gives us the story, the place, the people, the meaning. It tells us what happened and why it matters. It does not tell us, “This happened on December 25.”
That means Christians in later centuries had to decide when to remember and celebrate the birth of Christ. And once you realize that, you can understand why different traditions formed.
Some people try to guess the season based on details like shepherds being out in the fields. You will hear arguments for spring and arguments for fall. The truth is, those arguments can be interesting, but they are not strong enough to give us a firm day on the calendar.
So, if someone asks, “Was Jesus born on December 25?” the most honest answer is, “We do not know the exact date.”
How December 25 entered the picture
Even though we do not know the exact birth date, we can trace the origins of the celebration on December 25.
A key name here is Sextus Julius Africanus, a Christian writer who lived in the early 200s. In his writings, he placed Jesus’ conception on March 25. If you count forward nine months, that lands on December 25.
That does not prove Jesus was born then. It shows how some early Christians reasoned about the date.
Then, in the 300s, we start seeing December 25 show up as an actual celebration date in the Western church. The Catholic Encyclopedia notes that by the fourth century, Western calendars assigned Christmas to December 25, and that Rome was celebrating it on that date before the mid-300s.
National Geographic also summarizes the same broad development, that by the fourth century, December 25 had become the dominant date in the Latin West.
So, the timeline looks like this.
In the early centuries, there was no single agreed date for everyone. Then you see December 25 argued from a March 25 conception date. Then, in the 300s, you see December 25 being used widely in the West as the date for the celebration.
Two big explanations people give for December 25
When you look at history writing today, two explanations come up again and again. They are not mutually exclusive. More than one thing can be true at the same time.
The explanation based on March 25
This is the most straightforward explanation.
Some early Christians connected key moments in Jesus’ life to meaningful dates. One tradition placed the conception of Jesus on March 25. In some versions of the idea, March 25 also had symbolic meaning tied to creation itself. Then, nine months later, you get December 25.
The important thing to understand is that this is not a modern historian claiming a medical fact. It is ancient Christians doing theological math and symbolism in a way that made sense in their world.
It is a date chosen for its meaning and consistency, not one pulled from a birth certificate.
The explanation is based on the Roman winter season
The other explanation involves the world Christians lived in.
In the Roman Empire, late December was already loaded with celebrations. Britannica notes that in third-century Rome, December 25 was associated with the rebirth of Sol Invictus, the Unconquered Sun, which was tied to the winter solstice.
National Geographic describes how December 25 became dominant in the West by the fourth century, and it points to a mix of factors, including religious reasoning and the surrounding Roman festival world.
You will sometimes hear people say, “Christmas is just a renamed pagan holiday.” That is too simple, and it usually skips the real history.
A better way to say it is this.
Christians were choosing a date for a significant celebration in a world where late December was already treated as a special season. Some Christians used theological calculations. Some leaders may have found it helpful to place the celebration in a season when people were already thinking about light, hope, and the turning of the year.
Those ideas can exist side by side.
Why do some people celebrate Christmas on a different day
Now we get to the part that surprises a lot of people.
Even when everyone says “Christmas is on December 25,” not everyone means the same thing by that, because not everyone uses the same calendar.
This is where the Julian and Gregorian calendars come in.
In 1582, Pope Gregory XIII introduced the Gregorian calendar to correct the drift in the older Julian calendar. Over time, the two calendars ended up separated by days. In our current era, the difference is thirteen days.
That is why some Eastern Orthodox churches celebrate Christmas on what most people call January 7. They are keeping December 25 on the Julian calendar, which aligns with January 7 on the modern Gregorian calendar used in most countries for everyday life.
The Associated Press lays this out clearly: Many Orthodox churches observe feast days according to the Julian calendar, while others use a revised calendar that aligns with the Gregorian calendar.
So in a strange way, there is agreement and disagreement at the same time.
Many would say, “We celebrate on December 25.” They disagree on which calendar is being used to locate that day.
Why Christmas Eve feels like the main event in many places
So far, we have talked about dates on paper. Now let’s talk about the night we are living in right now.
In many cultures, December 24 is the heart of Christmas.
That can be for a simple reason. In many church traditions, major feast days begin at sundown, the night before. That is one reason why Christmas Eve services exist, and why midnight services became such a big part of the holiday in many places.
It can also be practical. Families gather when work is done. Meals take time. People travel. Night is when everyone can finally be in the same room.
And in many parts of the world, Christmas Eve has its own customs that are older than the modern idea of Christmas morning.
Some places have a special meal on the evening of December 24. Some have candlelight services. Some wait for a certain moment to begin—some exchange gifts at night.
So when you notice that Christmas is celebrated “early” in some places, it is not early for them. It is right on time.
So, was Jesus born on December 25
If someone asks me, “Was Jesus born on December 25?” I come back with an honest answer.
We do not know the exact date.
But we do know why December 25 became the celebration day in the West.
We know that early Christians used theological calculations tied to March 25, which, nine months later, landed on December 25.
We know December 25 also sat inside a Roman winter season already packed with meaning and celebration, including solstice-related ideas like Sol Invictus.
We know the Western church was celebrating the Nativity on December 25 by the fourth century.
And we know that calendar differences explain why some Christians celebrate what appears to be a different date today.
A simple way to think about it on Christmas Eve
Here is the way I like to hold it in my mind on December 24.
Christmas is not mainly about solving a calendar mystery. Christmas is about the birth of Jesus Christ, the arrival of the Savior, and the hope that comes with Him.
The early church chose a day to celebrate that truth, and over time, it became widely observed.
So on Christmas Eve, we can enjoy the build-up, the lights, the quiet moments, the family noise, and the last-minute details, without feeling like we have to win a debate about the exact day.
Setting up Christmas Day
Tomorrow, on Christmas Day, I am going to read the Christmas story.
Today was about the history behind the date and the season.
Tomorrow is about the message itself.
And that is a good way to do it.
Christmas Eve helps us get ready.
Christmas Day brings us to the story.
