How did Judaism survive the diaspora?
Two other related aspects of Judaism were quite important, too. First was that the Torah was central to Judaism, the reason Jews are called the people of the book. The fact that a book was more important to Judaism than any other physical object or place made it easy to carry the religion with people wherever they went. Little is more portable than a book. Second, the idea of having a rabbi-centered form of Judaism, rather than a priest-centered form of Judaism, allowed for a democratization of the religion and an independence from just one temple, a kind of decentralization, instead of a dominant priestly caste that was dependent on one temple in one place that could be and was destroyed. Rabbis were the teachers, not simply religious leaders, and as such, they ensured that all males (and now females, too) learned to read the Torah and observe all proper prayers and rituals. Had the religion not made this paradigmatic shift from priest to rabbis, so that all Jews could read Torah and be properly observant, it is quite possible that Judaism would be no more.
How could a religion with so few, that does not seek converts, and was constantly persecuted survive the loss of their homeland? The Romans expelled all Jews from Israel in the First Century, but the religion has survived the persecution over the years. The primary reason for the survival of the faith of Judaism is the sense of community that Jews have with one another. This fellowship was established by living in isolated communities that centered around the synagogue and the Jewish schools that were built. Jews followed a strict code of dietary and moral laws to develop this unity. They made it a practice to live within walking distance of the synagogue so they would have their own neighborhoods. The separation, over time, was forced but had no less an impact on developing cohesion within the faith. Within this community, the family was an essential element. Families and communities celebrated the weekly Sabbath together as well as the festivals of the Jewish calendar.