No Barriers

אך שמח לרבות לילי יו"ט אחרון של חג לשמחה.  Why is there an increase in simcha on Atzeret?  If Atzeret is a regel unto itself, why is it called Shemini?

Usually the word אך functions as a miut so how does it include the night for simcha?  The Gra explains it comes to exclude that there are no mitzvot and the command of והיית שמח is all that is left.  What we learn from here is that other holidays require some sort of mitzvah which enables us to obtain simcha but on Atzeret there is no need for external mitzvot, the day itself demands simcha.  What is the nature of this simcha?  

The number 8 always represents that which is above nature.  During the seven days of Sukkot korbanot are offered for the gentiles as well; they have a part in the natural cycle of the world.  Atzeret is just a korban for Klal Yisrael, it alludes to the times of Mashiach where the gentiles will have no power.  In the back of the Eretz Tzvi (Frumer) there are pieces from a grandchild of the Rodamskor (Emrei Chanoch) and he says in his grandfathers name that why is the mitzvah of simcha for Atzeret written just in the form of a hint?  The Rodamskor explains since Atzeret hint to the days of Mashiach it needs to be snuck in so that the evil forces don't try to attack the day.  How is Atzeret an allusion to the times of Mashiach?  

The simcha of Atzeret is the fact that a Jew is connected to Hashem irrespective of mitzvot.  Simcha comes about when things can come together.  The fact that Klal Yisrael is connected to Hashem, the fact that there is that bond, that closeness, which is experienced on Atzeret, obligates simcha.  That is what will be revealed in the times of Mashiach.  The apparent barriers that exist, that seem to impede on this connection will be broken down.  

However, this doesn't come about on its own.   It is only after אך, after the first 21 days of preparation during Tishray, and specifically during the 7 days of Sukkot that can culminate in a Shemini Atzeret.  It is only after we have one our part, have fulfilled the mitzvot, that Hashem allows us to jump to the Shemini, to the supernatural realm which is above our own grasp.   

The Emrei Chanoch adds based upon the Shem MiShmuel that the קללות that come אשר לא עבדת בשמחה are not a punishments, but a means to fire a person up to feel that desire to come back to Hashem.  With this in mind, he says ,since milah is done with simcha (see Shabbos 130) the golus that no dominion over it and it also hints to the times of Mashiach.  Hence, he adds, the seudah for a bris milah is also derived from a hint הגמל את יצחק (5+3 מל) (see Tosfos Shabbos 130a) to avoid the evil forces trying to attack.  In light of the above idea, it is the same yesod.  Milah is a symbol of one's bris, one's internal connection to Hashem and that hints to the times of Mashiach (see also Pri Tzaddik Sukkot #9, #12.)