What is Judaism? For most Jews it is how they express themselves Jewishly. However, over the millennia Judaism included sovereignty, a political structure, a military force, a priestly class, Temple worship, and of course religious observance. Following the destruction of the Second Temple, Jews were dispersed throughout the world and their welfare depended on the degree that the temporal rulers either needed their skills or felt compelled to persecute them because they were neither Catholic nor Moslem.
Following the French Revolution a new spirit of tolerance began to emerge in which Jews were (eventually) given full citizenship rights. Professor Batnitzky has deftly provided a primer on how the major Jewish thinkers from the eighteenth to the twentieth centuries defined Judaism in this new epoch of emancipation. Is Judaism only a religion based on the Protestant model of private ritual practice and articles of faith (i.e., be a Jew at home but a German in public)? What about the political structure and nationalism inherent in Judaism ? For Jews who maintained fidelity to Jewish observance this question may have been inconsequential. However, for the governments who were considering granting full citizenship rights to Jews, this was a very important question.
Jewish responses to emancipation took many different forms. The ways in which Jews viewed their Judaism corresponded to what the thinkers and writers of the times wrote about Judaism. Some practiced insulation and isolation, some tried to bridge the gap between modernity and Judaism, some felt that the old traditions were outmoded (Reform), some felt that only certain practices had to yield to modernity (Conservative Judaism), some explored all the facets of Jewish experience dispassionately with scientific rigor (Wissenschaft des Judentums), others turned to Hebrew and Yiddish literature and poetry, many were content to be cultural Jews, some were deeply engaged in the philosophical meaning of Judaism, still others dared to fan the flames of Jewish nationalism (Zionism) both religious and political. Needless to say, the Holocaust and the State of Israel have also had a role in defining Judaism.
One might quibble with certain minutiae of interpretation, but taken as a whole, How Judaism Became a Religion is an excellent introduction to the key philosophers and writers who influenced modern Jewish thought. Starting with Mendelssohn, the neo-Kantian Cohen, and proceeding to Rosenzweig, Buber, the Kooks, Hirsch, Kaplan, Soloveitchik, Levinas and Fackenheim, with many detours to other writers and thinkers, Prof. Batnitzky has presented a valuable volume which frames the questions that produced contemporary Judaism.
A lot of material is covered in this slim volume, and the annotated bibliography at the end of each chapter provides sources for more detailed reading. The book is an excellent overview of one aspect of modern Jewish thought.