Secular Judaism has existed as an alternative form of Jewish life for over two hundred years. A major impetus for this has been the Shoah, but the roots go far back in history. After the destruction of the Second Temple in 70 C.E. the priesthood eclipsed and rabbinical Judaism became ascendant. Rabbinical Judaism, i.e., faith based on Torah study and interpretation as well as Halachic rulings are credited with keeping the Jewish people together during the Diaspora. In the 12th century Maimonides produced the Mishna Torah, a rational analysis of revelation. A towering intellect, Maimonides writings and philosophy had a major impact not only on Judaism but on Christian dogma and Renaissance thought in general.
In the 17th century Baruch Spinoza took up where Maimonides left off.
A major issue for Spinoza was what he considered to be a rational relationship with G-d. Spinoza argued that the Tanakh should be read as a method of understanding Jewish belief at successive stages of development.
He wrote, "Knowledge of G-d is not based on books but on the idea transmitted to the prophets of the Divine Mind," i.e. "obedience to G-d and and the practice of justice and charity. His views were seen as opposition to Rabbinic authority and in religious court he was excommunicated. Yet so overwhelming was his intellectual power that his work is considered to be the foundation of the philosophies of Descartes, Newton, Locke, Voltaire and Kant, each of whom in their own way followed in Spinoza's tracks. Zionism is considered by many to be the intellectual prodigy of Maimonides, Spinoza and Mendelssohn(the father of Jewish Enlightenment).
Although none of these thinkers were secular, they are widely credited with providing the intellectual foundation of secular thought.
From the 19th century onwards more and more Jews began to equate Judaism not with Religion but with a culture, a way of life.
Secular Jews believe in reason and reality, that is, the power of humans to solve their problems.
They believe that every human being deserves life, freedom and dignity.
They believe in the value of Jewish identity, separation of church and state as well as the survival of the state of Israel.
The question then is whether secular Judaism is a threat to the continued existence of the Jews, a positive development, or merely another expression of variation among the Jewish people.