Every time I look at you
I don't understand
Why you let the things you did
Get so out of hand
You'd have managed better
If you'd had it planned
Now why'd you choose such a backward time
And such a strange land?
If you'd come today
You could have reached the whole nation
Israel in 4 BC had no mass communication
The believer asking why God picked exactly that moment in human history to send his Son to Earth for the redemption of sins, and the non-theist wondering why this one movement that began in an obscure corner of the Roman Empire took off when so many others didn't are both asking the same question.
Why Jesus in Galilee and Judea just then?
Curiously, I think both questions have the same answer, which is--more or less--Roman roads and the Hellenization of Asia Minor.
The Hellenization process that followed in the two centuries after Alexander the Great created an overlay of cultural unification that spread Greek language, ideas, and city-states from southern Italy as far as the Indus River valley. The Romans then moved in on the western part of that Hellenized world and enforced a political unity forged with the pilum and cemented with a network of military roads.
It does not do to forget that the lingua franca of the eastern Roman Empire was always Greek, not Latin.
It is also critical to recall that, in an imperial population of 60 million, about ten percent were Jews, many of them Hellenized (Greek-speaking) and spread out of Judea in the diaspora.
There is considerable evidence within the New Testament (excavated by such critical historians as John Dominic Crossan) that Hellenized Jews were among Jesus' early followers and Christianity's earliest evangelists.
Hellenized Jewish and Gentile culture provided a sufficiently uniform context in which to spread a radically modified Jewish belief system, while the Pax Romanum and those wonderful military roads created both the international stability and the certainty of travel necessary to spread the creed.
For all that, it was a narrow window. Two great modern religions--Christianity and Rabbinic Judaism--originated in the brief interim between the death of Herod the Great and the Jewish Rebellion that ended in 70 AD--during the stable Augustinian peace that people foolishly thought might last forever.
So back to my question (because I could go on for far too long, as it is an interesting subject that has given rise to many quality books):
Why Jesus, then, in Judea under Roman rule?
The answer: that is the earliest possible point in western world history when the necessary matrix of dependable communications, political stability, and widespread cultural coherence existed to allow such movement to spread and institutionalize.
If you're Christian: God sent Jesus into human history at the first moment at which the structure of society would allow the Word to spread.
If you're not: The first global evangelical religion appeared just as soon as the cultural, political, and economic situation permitted it: Jesus (and Paul) just happened to be the lucky beneficiaries of timing.
And what's that all got to do with Christmas, anyway?
Probably not much.
But, hey, I'm a semi-devout Catholic pragmatist Libertarian. What did you expect?