There are two stories about Jesus’s birth in the NT. One at the start of Matthew, the other at the start of Luke. They are very different in many regards. I wrote more about these in other places at Christmas, so I won’t recap too much about their content.
Because the stories are in some ways similar and in others completely different (and contradictory – unless you jump through some bizarre exegetical hoops) they give us a lot of data. From a source critical perspective, when you have two different accounts of the same thing, you typically divide the story into three sources: those sources that belonged to each individual (Matt and Luke) and the sources they both knew and drew on.
In this latter category, for the birth narratives, seems to be a set of interesting features, including:
1. Jesus came from Nazereth.
2. The Messiah comes from Bethlehem.
3. Jesus is the Messiah.
4. Jesus was born around the turn of the CE.
5. Jesus’s parents were named Mary and Joseph (Miriam and Yosef if you degreekify them).
Clearly 1-3 are a problem! And so many scholars believe that the birth narratives are motivated by the desire to resolve 1-3. To show how, even though everyone knows Jesus comes from Galilee, he must have been born in Bethlehem. And this is where the common source gives out. Whatever it was, it didn’t resolve the issue, because Matt and Luke each take a stab at squaring the circle and do so in different ways.
I’m posting on this topic because of imarriedaxtian’s comment in the previous post. I said that we can use the birth narratives as evidence of the dating of Jesus’s birth, even though few scholars think they are anything but mythological inventions. This is point 4, above.
We can deduce 4 because the *rough* dating is common, and therefore likely to be an earlier tradition. I say rough because, as is commonly pointed out, the disparities in the two accounts mean that they can’t both be exactly right – the dates just don’t line up. This has been pointed out many times, and is a favorite tool of ridicule by some atheists, who unfortunately stop right there and fail to think through the issue.
Having the dates not match exactly is not really surprising if you follow the standard model described above – both writers (or sources only they knew) are making up their birth narratives much later.
What is significant is that they both plump for the same kind of period. Imagine if you read two accounts of the birth of a famous man from the middle twentieth century. One places his birth in 1920, the other in 1926. From that I think you can probably say that the evidence points to a birth somewhere in the early 20s. Clearly the evidence does not support a birth in the 40s. You could deduce further that the two accounts don’t agree, they both can’t be right, and it may be that neither is correct. But the balance of probabilities suggest that the 1920s is the most likely period.
So the birth narratives give us evidence on the dating of Jesus’s birth, even though we don’t trust the specific dating that either gives us.
Of course, as I said in the previous comment, there are other threads of evidence for the dating of Jesus’s birth – just as (if not more) speculative, but contributing to a consensus view that Jesus was born somewhere around the turn of the CE.