Why were Nadav and Avihu, two of the sons of the high priest Aaron, killed? Why did their death come by fire? What is the significance of the fact that the two brothers died at the same moment? And why did Aaron, in the face of the loss, remain silent—become wrapped in silence? What of the response of their mother, Elisheva, who is not explicitly mentioned in the text? And why is the death of Nadav and Avihu referred to in the Torah reading for the holiday of Yom Kippur, the holiest day in the Jewish calendar? This is the second lecture of the 27th year at the Y, and this year marks a change of format. In previous years the second lecture has been devoted to a portrait of one or two Talmudic masters. The focus continues to be Talmudic, by way of its commentaries on this disturbing episode. But the change from one format to another is warranted since there is less material on other masters—which is not to say that they are less important. Though some commentaries presume Nadav and Avihu to have committed a sin that brought a death sentence, the general view is that they were striving for a higher degree of religious fervor. While their father remained silent, their mother, according to the Midrash, shouted and cried—and moved Aaron the father to cry as well. Another commentary depicts Aaron as protesting the injustice of their death. The death of the brothers is referred to on Yom Kippur in order for us to understand that sometimes we cannot understand. In the end we join our silence to that of the father Aaron—and continue to look for the answers hidden within.