What is the importance of the "higher" כתר coming and infusing the "lower" מוחין and מדות? Is it only that the "higher" receives from giving to the "lower"? Or is it, as the רבי makes us aware, because in the perspective of Hashem's Essence there is no "higher" and "lower"?

This is the newfound appreciation of עצם: An עבודה of ביטול, of rejecting all perspectives - even spiritual ones - of self and self-perfection, and embracing the perspective of Hashem's Desire of having a דירה בתחתונים.

This is the message of "כולן שוין לטובה", and with this the רבי answers the questions from the beginning of the מאמר and fuses together the explanations of חסידות and רש"י on this fundamental פסוק!