The primary reason the birth of Jesus took place in Bethlehem was to fulfill the prophecy given by the minor prophet Micah.
2. "And you, Bethlehem Ephrathah, you being least among the thousands of Judah, out of you He shall come forth to Me, that is to become Ruler in Israel. He Whose goings forth have been from of old, from the days of eternity" (Micah 5:2, Holy Bible in Its Original Order throughout)
The interest thing about our Savior's birth is how God used the powerful but sometimes brutal Roman Empire, coupled with a Jewish fixation on their ancestral lineage, to fulfill a 700-year-old prophecy!
Before they left their hometown, Mary was betrothed, but not married to, Joseph. As a side note, betrothed women had many of the same legal rights as those who were married except that they could not have sex until after the wedding.
Mary and Joseph had to go to Bethlehem due to Roman taxation policies. From time to time, the Romans conducted a census not merely to count people but also to find out what they owned so that they could be taxed. It was decreed in the year Christ was born (5 B.C.) that such a taxation census would be taken of the people.
1. Now it happened in those days that a decree went out from Caesar Augustus (the first true Roman Emperor who ruled from 27 B.C. to 14 A.D.) that all the world should be registered. 2. (This registration first occurred when Cyrenius was governor of Syria.) 3. Then all went to be registered, each to his own city. 4. And Joseph also went up from Galilee, out of the city of Nazareth, into Judea, to the city of David which is called Bethlehem, because he was from the house and lineage of David (Luke 2)
Why not do it at home?
Why, in Palestine, did the Romans not carry out their census where people lived as they did for the rest of the Empire? Why did the parents of Jesus have to make the more than 80-MILE (about 129 kilometers) journey to Bethlehem?
For Jews, especially those who lived after the return of Judah from Babylonian captivity, tribal identification and line of descent were all-important. We find in the New Testament the lineage of Jesus traced back not only to Abraham (in Matthew 1) but also to Adam (Luke 3). The Apostle Paul wrote about his own lineage (Romans 11:1). In fact, he used it BEFORE his conversion as a way to think of himself better than others (Philippians 3:4 - 7) and AFTER conversion as a tool to combat those who were false ministers (2Corinthians 11)! The self-righteous Jewish Pharisees used their physical lineage to boast how spiritually superior they thought they were (John 8:33 - 39, see also Matthew 3:9).
Roman law, in deference to Jewish customs and prejudices (plus the desire to, as peaceably as possible, collect taxes from a subjugated people), stated any census in Palestine would be undertaken based on the town from which a person's ancestral family belonged. In the case of Joseph, since he traced his lineage to David, who was born in Bethlehem (1Samuel 17:12), he had to go to the city for the census.
What time of year did it occur?
What time of the year did the census in Bethlehem take place? Was it in the middle of winter, as many assume because of its ultimate link with Christ's birth and Christmas?
"In his account of the birth of Jesus Christ, Luke records a major historical event of that time . . . The taxation and census decree by Caesar Augustus was carried out according to the Jewish custom which required that such taxes be collected after the fall harvest. Thus, Luke’s record of this taxation reveals that the birth of Jesus took place during the AUTUMN" (Holy Bible in Its Original Order, Appendix E)
The Romans conducted censuses in Palestine during the fall so that they could maximize the amount of tax revenue they collected from the people. Barney Kasdan, in his book God’s Appointed Times, wrote regarding Rome and its taxation policies that they took censuses at a time convenient based on local customs. In short, it was far better for the Romans and Israelites to handle taxes in the fall of the year as opposed to the middle of winter.
When it came to taxes, Rome knew what it was doing. It commanded a taxation census be taken when the people of the land had the free time (right after the big fall harvest), the money (from the harvest), and weather to permit them to travel. Carrying out such a census in the cold of winter, when travel was difficult (and people had more excuses), does not make much sense. God used Rome's desire to collect as much tax revenue as it could, coupled with a Jewish fascination of their ancestors, to fulfill an awesome prophecy concerning the birth of Jesus in Bethlehem!