The Kohen Gadol's special clothing on Yom Kippur was never used again, even on a future Yom Kippur. What does this teach us about the “mechanics” of atonement. How can a person “undo” his past?
To understand this, we must come to a better understanding of what the Rambam writes that a true penitent is actually not the same person he was when he sinned.
Based on Likkutei Sichos vol. 28, pp. 224-5.