The phrase, “once a year,” underscores the significance of Yom Kippur. We find a similar idiom regarding the festival of Succos. The Torah declares, “You shall celebrate it as a festival for Hashem, a seven-day period in the year” (Vayikra 23:41). It seems that these two Yamim Tovim, festivals, distinguish themselves in that their hashpaah, spiritual influence, is to endure for “the year.” Horav Mordechai Ilan, zl, notes that this idea applies only to Succos and Yom Kippur. The parallel that exists between them is that the avodas Hashem, service to the Almighty, which is intrinsic to these festivals is powerful enough to inspire us for “the year.”
On Yom Kippur, we serve Hashem through yiraah, fear, as we achieve an unprecedented plateau in our spiritual relationship with Him. Yom Kippur lasts for only one day, but its spiritual influence is to carry us through the entire year, until the following Yom Kippur. On Succos, we serve Hashem through simchah, joy. We experience the joy of serving Hashem in such a unique manner that it should last a whole year. The word, “bashanah,” presents a new dimension in our avodas Hashem during these festivals. If we realize that our experience must carry through the entire year, we will place greater emphasis on our avodas Hashem during the Yom Tov.
