On his deathbed, Hillel the Elder blessed Reb Yochanan ben Zakai, the youngest of his students, to become "av l'dorot" - the father of the generations. The blessing was indeed fulfilled. Because of his great foresight in preserving the yeshiva at Kerem b'Yavneh, Rabbi Yochanan ben Zakai emerges as a Torah giant whose life and work guaranteed Jewish survival in the exile.