Ethical monotheism is indisputably the foundation of Judaism, its intellectual core. No matter how pure and grand that concept is, however, I do not believe that it alone would have sustained the Jewish people throughout the centuries of exile, hardship and persecution.
Something else has held the people together and nourished their souls: Shabbat, the Jewish Sabbath. Throughout our generations, the Jewish people have kept Shabbat as a sign of our covenantal relationship with the Eternal One. In so doing, we introduced into the world the concept of ‘sacred time’. After the ethical teachings of the Bible, I would say this is the most important gift our tradition has given us.