The rosh of the shana, because it is the “head” of the unique “body,” contains within it, as in a single thought, all the days of the year.
For this reason, good spiritual work on Rosh HaShana forms a better inner picture of the year’s shape and character.
This does not mean, however, that on Rosh HaShana one should make plans for the whole year.
That would be impossible, for an entire year is multidimensional and is connected to many different worlds.
What one should do on this day is form a general picture of what ought to be the character and direction of this year.
One should place on the head of the year a “crown of kingship,” and thereby transform the year into a completely different form of being.
This spiritual work must be done not only in honor of the day, but also because of the influence that the “head” of the year exerts on the entire “body” of the year.
On Rosh HaShana, a person has it within his power to impart life-force to the whole year.
This is the reason for the custom not to sleep during the day of Rosh HaShana, as cited in the halakhic literature in the name of the Yerushalmi:
“One who sleeps on Rosh HaShana, his mazal will sleep.”
Sleep on Rosh HaShana puts the whole year to sleep!
–Rabbi Adin Steinsaltz