It is true that Yom Kippur completely atones for a Jew. But looking deeper, it is more accurate to say that it completely atones for one at the level he is currently holding. Since there are many levels to teshuva (repentance), we cannot possibly wipe out all of our mistakes at once. Initially, we did not realize the gravity of our actions. When we begin to realize the seriousness of our deeds, we are aroused to return to God. Yet as we grow spiritually, so does our awareness of the greatness of God. When we do teshuva, we are purified and ascend to a higher level and our perception of God is correspondingly heightened.
At this stage, we need to repent for our more inferior perception, which is now considered "material" compared to our relatively higher spiritual awareness. We now understand that our deeds were more serious than originally thought. Therefore, we need to ask forgiveness again according to our new level. Practically, this means that there are times we need to recall old misdeeds we thought we were finished with and repent on a level consonant with our newer spiritual level.
Not only that, due to our limited perception at the time of our misdeed, it was as if we "limited" the God's honor (in our own minds). We now must repent for this seeming insult to God's honor. If God is called Ein Sof, the Unlimited One, how can we understand the true depth of what that really means? For this reason, the process is endless. We must ascend higher and higher to attain greater levels of understanding the greatness of the Creator.
This is the dynamic of Olam HaBa, the World to Come, a continuous coming close to the Endless Light.
From a recent shiur of Rav Ephraim Kenig, shlita, based on Likutey Moharan 6:3.
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