Every year there descends and radiates a new and renewed light which has never yet shone. For the light on every year withdraws to its source in the Essence of the Ein Sof on the eve of Rosh Hashana, ‘when the moon is covered.’
Afterwards, by means of the sounding of the shofar and the prayers, a new and superior light is elicited… a new and more sublime light that has never yet shone since the beginning of time. Its manifestation, however, depends on the actions of those below, and on their merits and penitence during the Ten Days of Teshuvah.
– Tanya, Igggeret HaKodesh, Chapter 14