The meaning of the
words Rosh HaShana literally is "Head (beginning) of the year." However, this
holiday carries much more significance than merely being the day on which a
new calendar becomes necessary.
The Sefer HaChinuch explains that Rosh HaShana is the day on which the whole
world is judged. Each individual creature is judged as an individual. This
judging has been compared to sheep passing in single file under the watchful
eye of the shepherd. Just as each sheep is scrutinized alone, separate from
the flock, so too are we judged on Rosh HaShana, as individuals, separate
from everyone else.
Why do we have a day of judgment? The Sefer HaChinuch explains further that
this holiday on which we are judged is truly a kindness of Hashem. Hashem,
because we have this yearly holiday, reviews our deeds yearly, thereby
preventing our sins from amassing. As we "only" have to deal with our sins
one year at a time, there is still room for repentance and atonement.
Furthermore, as Hashem judges us with kindness, if there are few sins, they
are pardoned. If there are sins for which punishment is needed to cleanse the
person, the punishment is exacted in small doses, bit by bit. If the
accounting of our deeds did not take place on a yearly basis, our sins would
accumulate until the point that Hashem would decide to end the existence of
the world, because of all the evil and disregarding of His words.
Rosh HaShana is the day which ensures the continued existence of the world.
It is therefore fitting to have this day as a holiday. However, as this is
the day on which we are judged, it is only proper that we conduct ourselves
on Rosh HaShana with a level of fear and awe not seen on other festivals.
This is the reason why we do not say "Hallel" (a special prayer of praises of
Hashem): It is not fitting for a person to sing songs of praise while
standing in judgment.