On the holiest day of the year, Yom Kippur, we come to Hashem in our most vulnerable state. We have no distractions like food or drink, soothing ointments or leather-made shoes. For 25 hours, we lay it all on the table, every bad decision, mean word, judging demeanor, lie, and mistake we’ve made — and we show it all to Hashem. In turn, when we expose the most intimate part of ourselves, stripping away every aspect of our character to experience our true, soulful selves, Hashem says, “I see you, I forgive you, and I love you.”
In the last Mishnah of Masechet Taanit, Rabbi Shimon Ben Gamliel says, “There were no happier days for the Jewish People than Tu B’av and Yom Kippur” (30b). Rav Judah Dardik explained that the simcha (happiness) of Yom Kippur emerges from the reality of our relationship, in which Hashem sees us in our most intimate states and loves us all the same.
There is another thought that seems to complement the previous one very well. Rav Judah captured the happiness of Yom Kippur through the lens of us and Hashem, and there can also be a pure simcha that emerges from our relationship to ourselves.
An overwhelming portion of Yom Kippur is spent on self-reflection, being genuine with who we are and who we have been. Specifically, we recount all of our missteps throughout the year (and even in life, according to some), as mentioned above. Of course, we can deeply appreciate how this adds a new dimension to our relationship with Hashem, but how can we say we change from this process? For many, it can feel like the focus on all we’ve failed in can be depressing, inducing the reality of our constant imperfection into our minds. However, such a notion is sorely misguided and misses a central goal of this process.
In his “Yesod Blocks” series, Rav Zev Bannett says that on Yom Kippur, when we’re confessing all we’ve done wrong, we’re actually doing something much more significant, albeit discreet. By admitting and regretting what we’ve done, we gain something new: acceptance.
Rav Bannett explains that Yom Kippur propels us to rise above our mistakes, to recognize that we are not defined by our shortcomings or our failures. In fact, we need to realize that every event in our life was an instrumental part of our growth. Moreover, when we stop identifying with our faults, we experience ourselves in our truest essence: as souls, connected to Hashem in an unbreakable bond like rays of light to the sun. When we live as souls, we remember that we are unconditionally valued and loved by Hashem; now, we need to live like that.
“[The] hidden self, the unconscious self, has endless courage, life and strength,” Rav Kook writes. “In truth, from the storehouse of one’s inner health, a person has enough power to influence the conscious and surface level of the self. It reminds the misleading voice that accuses oneself of being sick and broken that in reality, one’s essence is brave, healthy, and full of life and strength” (Maamarei Hareiyah, p. 156).
Yom Kippur is the happiest day of the year because it renews our sense of self. For 25 hours, we ingrain into our minds that Hashem loves us no matter what, and we are reinvigorated with our unconditional self-worth. What’s not to be happy about?
 As translated by Rabbi Ari Ze’ev Schwartz in “The Spiritual Revolution of Rav Kook,” p. 59