A day of repentenance and atonement, much like Lent for Christians like me. All are serious times, in which to take life very seriously - dead seriously - as this precious and brief gift of life deserves to be taken for at least some days of the year before we revert to our normal ways and habits.
We are all just animated dust, with God's spark. It's easy for me to forget that during daily life, when everything seems so important.