The Hebrew worldview was very simple, family-based, grass-roots, and relationally oriented. On the other hand, the Greek worldview [Hellenism] was hugely philosophical, intellectual, pagan, and political. These are obviously over-generalizations, but bare with me. What God knew in His great wisdom is that testimonies written [the NT] from a worldview birthed by the marriage of Judaism and Hellenism would produce a message translatable to any worldview in any culture at any time and in any place. More simply put, 1st century Palestine was the most fertile soil for the Gospel to be originally planted because of its natural cultural fabric. I believe that this was the case on many fronts: political, spiritual, philosophical, theological, moral, etc.
In his book "The New Testament and the People of God" [pgs 359-360], Tom Wright seems to agree. He points out that "the single most striking thing about early Christianity is the speed of its growth." Wright continues,
Christianity did not spread by magic. It is sometimes suggested that the world was, so to speak, ready for Christianity: Stoicism was too lofty and dry, popular paganism metaphysically incredible and morally bankrupt, mystery-religions dark and forbidding, Judaism law-bound and introverted, and Christianity burst on the scene as the great answer to the question everyone was asking.
Wright goes on to say that the primary reason for the rapid spread of early Christianity was that these first Christians "believed that what they had found to be true was true for the whole world" - that Jesus was King and Lord.