If Judaism can change, what must remain constant? Solomon Schechter, who became the President of JTS, identified the core elements of Judaism that unite all Jews who are part of the tradition, across ideologies and across time. Mordecai Kaplan, a professor of Midrash at JTS, took these elements and interpreted them as constituting a civilization that, he proposed, could be embraced by modern American Jews.

Further reading:
Solomon Schechter, “Historical Judaism,” “Excerpts from Seminary Addresses,” and “The Work of Heaven,” in Waxman, Tradition and Change (89-109, 163-172)
Mordecai M. Kaplan, Judaism as a Civilization, (3-15, 173-208, 431-435);
The Meaning of God in Modern Jewish Religion, Chapter 1