Sukkot is very deep. The holiday comes from the Jew when s/he is in a totally pure place after Yom Kippur. This festival continues the natural and hard-worked progression from when we crowned Hashem King over us on Rosh Hashana, though the ten days of repentance, through Yom Kippur. Sukkot is our return to the deepest place in ourselves that has never been contaminated and is not affected by others, the place that is who we really are.
Rosh Hashana and Yom Kippur are days of awe; during these we come back to Hashem out of fear of our judgment and destiny. But this is not the greatest form of teshuva (returning, repentance). For a person who returns to Hashem and repents out of fear, the sins are indeed forgiven; but when repentance comes from love, sins become merits!
Reb Levi Yitzchack of Berditchov Z'tzl says on Rosh Hashana we do Tashlich and throw our sins away into running water because, although the sins are forgiven and considered as if done unintentionally, still, even sins committed unintentionally are sins, and so we do no want them. But on Sukkot, when we repent, we repent out of love for Hashem, and now our former sins can become merits. Now, realizing that when we threw out what we thought to be sins but what really could be merits, we want the sins back from the water. Therefore, we do Nisuch Hamayim. In this ritual, we pour water on the Altar at the end of Sukkot; and so we regain the water with the once-sins-could-be-merits and offer up the sins with love before Hashem.
May we all merit to do teshuva out of burning love for Hashem -- a deep love developed out of the fear and awe before Hashem already deeply rooted in us with Rosh Hashana and Yom Kippur. And may we combine love and fear in a deep harmony. In that same vein, may we know how to react with power or kindness, or a combination of the two, based on our situations, even if by nature we would react one way to everything.
Have the sweetest and most joyful Sukkot, and may we all meet in Jerusalem This year (... we keep saying next year in Jerusalem, every year….) for real!