Rabbi Nachman teaches,
The joy of the three major festivals, Pesach, Shavuot and Succot, gives us a share in the Inner Light of G-d, bringing new life to the mind and soul and enhancing our perception of God.
On the festivals we should return to G-d out of joy. On each of the festivals the world is judged ( Rosh Hashanah 16a) . A time of judgment is a time to return to G-d. Through repentance, the forces of holiness are released from the hold of the evil husks, speeding the final redemption.
Likutey Moharan I, 30
With permission taken over from: Daily Dose Of Rabbi Nachman