How the division of the annual energy that is drawn down on Rosh Hashanah takes place:[1]
All of the life and energy on behalf of the entire year is drawn down on Rosh Hashanah as man was created on Rosh Hashanah. This energy is then divided into 12 parts, one part on behalf of each of the 12 months. Each month receives the life and energy that was designated for that month from the general energy that was designated for that entire year on Rosh Hashanah. Likewise, each day a portion of life and energy that has been designated for that day is received from the general energy designated for that specific month. Each year receives a special designated energy and life that was not received in the previous years. [In the next discourse of Sos Asis, the Alter Rebbe explains in greater detail that aside for the life force being divided into 12 parts, one part per month, it is also divided based on the festivals and seasons. In his words:[2]] This life force is also divided between the three festivals [i.e. Sukkos, Pesach and Shavuos], and the four seasons [i.e. autumn, winter, spring, and summer] as well as the four times that the world is judged [which is on the first of Tishrei which is the judgment of all creation, the 15th of Tishreiy which is the judgment on water, the festival of Pesach which is the judgment of grain, and the festival of Shavuos which is the judgment of fruits.] Only after the life force for the entire year is divided on behalf of the above three divisions [i.e., festivals, seasons, and judgment days] only then is it divided to the 12 months and afterwards to each individual day, and even to individual moments within the day.
[1] Likkutei Torah p. 46a
[2] Likkutei Torah p. 47a