On Yom Kippur an especially sublime light emanates from the upper worlds, and even the Accuser is unable to make accusations. Yom Kippur influences the entire year, and therefore one should greatly rejoice as it approaches.

A day like no other:

Because Yom Kippur is like the World to Come, and it is a day that is more special than all other days of the year, as they said…with regard to the verse: “‘Of the days that were created, one is His’ (Psalms 139:16), this is Yom Kippur,” on which there is illumination from the upper world. Even the Accuser is not permitted to make accusations.

Yom Kippur influences the entire year:

Therefore, this day illuminates all the other days…and likewise, this day elevates all the other days…meaning that this day elevates all the other days to a level that is above nature, like it is explained in another place, that existence is dependent on the ability to nullify [the self and to cleave] to the transcendent source [of all things]. Therefore, one should rejoice when this holy day approaches…and illumination is channeled through this joy from Yom Kippur to all the other days. (Rabbi Yehuda Aryeh Leib Alter, Sefat Emet, Yom Kippur 5652)

Further reading: For more on resembling the angels on Yom Kippur, see A Concise Guide to the Sages, p. 231; A Concise Guide to Halakha, p. 169.