Hi,
The Zohar equates Purim and Yom Kippur (which is called
"Yom haKippurim" in the Torah).
The Piaseczner Rebbe, writing in the Warsaw Ghetto,
explained: Just as one is obligated to repent and fast on Yom Kippur, so one is
obligated to be joyous on Purim!
Have a great day,
Mordechai
