Withdrawal is a choice. Sometimes we need to make the choice to withdraw from the world around us to process something which has just happened. Sometimes we are even advised to make that choice. Sukkot feels like just such an instance. After the grandeur, the majesty, and the excitement of Rosh HaShana and Yom Kippur, we take some time to celebrate a festival whose largest component happens at home, with our families.
What do we do when Rosh HaShana and Yom Kippur lacked the pomp and ceremony which we are used to? What do we do when, of necessity, we withdrew for Rosh Hashanah and Yom Kipppur? We don't need to withdraw anymore. We don't even want to withdraw anymore. Sukkot has an answer for this as well. While normally Sukkot has a stronger emphasis on family dinners and on private enjoyment in the (relative) comfort of our (temporary) homes, Sukkot is also the festival of internationalism and of celebrating our humanity.
The prophets tell us that when Moshiach comes all nations will come to Jerusalem for Sukkot, build Sukkot, and partake of the festival with us. The reason is that the basic message of Sukkot, the uncertainty and lack of control inherent in the human condition, is a message relevant to any member of the human race. By living in our Sukkot, eating in our Sukkot, sleeping in our Sukkot if we are able, and in general spending as much time as possible in our Sukkot, we learn again the message that we can't control everything in our lives. We learn this basic truth from the fact that no matter how much we don't like it, if it rains, gets too cold, or the mosquitoes start to really bother us, we will have to go indoors. Our ability to remain in the Sukkah as we are commanded to is contingent on factors completely outside of our control, and making peace with that fact is the central message of the holiday.