"Yom Kippur is...looking in the mirror and seeing what you're going to look like after you've died."
Picture people running around, sneaking up behind one another with a big ram's horn, giving it a blast, as if to say, "Wake up! It is upon us again." The liturgy of Rosh Hashanah is designed to get you to wake up and pay attention not only to who you are, but to who you have been and who you mean to be.
Yom Kippur is not eating, not drinking not sleeping very much, not having sex, not dressing in fine clothes and looking in the mirror and seeing what you're going to look like after you've died. And the most joyous noise a Jew can hear is the sound of the shofar announcing the end of Yom Kippur, because it means that you have lived through the day of death and not died.
Rosh Hashanah is about reverence and gratitude for life, the mother lode of all religious insight. Yom Kippur is about telling the worst truth about yourself, and getting new life from that.
from Rabbi Lawrence Kushner