Naftal Tzvi Horowitz, the Ropschitzer Rebbe, 1760-1827, comments on the holiday of Succot by employing the traditional metaphor of shadow in his book, Zera Kodesh, Volume II, p. 56, ‘First Night Succot’ (my rendition):-
‘You shall dwell in succot’, et al. and we know that Chazal, our Rabbis-Of-Blessed-Memory, refer to one sitting under the schach as being in the shade and the Zohar terms that shade צלא דמהמנותא, the shade of faith. It is used in the Talmud as well, based on this verse in Isaiah 4:6 – “And there shall be a booth for a shadow in the daytime from the heat”.
But there’s a problem. As the law of physics indicates, a shadow is formed not when someone is directly under what casts the shadow. The object, and in our case, the person seeking to fulfill the mitzva of being in the succah, can only create a shadow by distancing oneself. That, however, would seem to defeat the purpose of the essence of the mitzva. One should be, at this holiday time of joy, as close as possible to God, to his instructions, to his purposes for life.
All man’s movements, or, in other words, his actions and deeds, are what create his shadow and, in creating a shadow, his actions and deeds can be observed and judged. What man does on earth is what bestirs on high just as what man perceives and comprehends what is intended from on high, above, is what causes him to do what he does on earth, below.
This line of influence, a mutual line of thought and doing, from up to down and from down to up, is one that is imagined through the miztva of the succah. In essence, our “shadow”, that tracing of our deeds, should be, must be, in direct parallel to the heavenly succah so that the shade cast from above will favorably influence us here on earth.
And similar to the laws of the holiday, that there must not be any partition between the sky, whether the sun or the stars (and the Ropschitzer employs a zoharic interpretation of the Hebrew כוכב as being read כו כב which is God’s name in a certain inner manipualation of the letters), that need be seen just enough, and the person under the schach must not be too much in the shade for otherwise it is as if one is being shaded by the wall and not from above (as the very first page of the Tractate Succah above reads: “but with one higher than twenty cubits he sits, not in the shade of the booth but in the shade of its walls”), so too our faith and commitment must originate and be motivated by as direct a connection as possible between what is above and we below.
We need the light that shines and enriches and provides to better ourselves. The succah, then, actually represents the entire Torah for us.
(spoken at the succah of the Spetter family, Shabbat Chol Hamoed, 5772)