At the end of the first chelek of the Zohar, in Parshas VaYechi, daf 250a, Rebbe Shimon bar Yochai speaks on the inyan of Kos Shel Brocho (Cup of Blessing) and bread that is left on the table for Birkas HaMazon.
It says there that Rav Hamnuna Saba would not give the Kos Shel Brocho to anybody else to bentsh, which then begins a wonderful Torah that we can learn much from.This particular use of a cup of wine, being the kos shel brocho, is alluded to in the verse from Tehillim כוס ישועות אשא “The cup of salvations I lift up,” because through this particular kos the blessings and salvations from Above are drawn down to Malchus. The cup is Malchus, and within the cup is wine, which alludes to Five Gevuros. We have to have on the table for Birkas HaMazon both wine that was set aside for this purpose, along with bread that was eaten from during the course of the meal. Klal Yisroel is called a Kos Shel Brocho, and like a Kos Shel Brocho is filled with wine, so is Klal Yisroel filled with the Yayno Shel Torah, the Wine of Torah, which is the wine of Binah. We say the four brochos of Birkas HaMazon over the Kos, which leads to it being a vessel for the “Resicha Kadisha,” Holy Chariot, consisting of North and South, East and West, which serve as allusions to the Sefiros of Gevurah and Chesed, Tiferes and Malchus, respectively. The bread then left on the table changes in spiritual essence from Lechem Oni, the Bread of Poverty, to Lechem Panag, which is fatty tasty bread, due to having Birkas HaMazon recited over the cup of wine. The way this functions is through Malchus becoming connected to the first three of the lower sefiros, Chesed, Gevurah, and Tiferes, which occurs through the facility of the Kos Shel Brocho, which is filled with the Wine of Torah, which is the Wine of Binah; Binah is the Mekor HaBrocho, the Source of Blessing. Through this a person is guaranteed to always have food on their table.
That’s a summation of that section of the Zohar, which translation thereof never really gets the idea across but it can get somewhat close. What we can draw out of this, outside of the supreme importance of always bentshing on a Kos Shel Brocho, is a great Sod in avodas Hashem. When it comes to Torah, we always must run to learn it for ourselves, like Rav Hamnuna Saba taking the Kos Shel Brocho for himself; this refers to making the Torah our own through chiddushim (novel thoughts) and writing kuntresim and seforim, like Rebbe Nachman talks about. While wine in its original state is the embodiment of the Chamisha Gevuros, the Five Gevuros, the wine can be elevated to the state of Yayin Shel Binah, Wine of Binah; this is primarily accomplished through using wine for purposes of mitzvos, such as Kos Shel Brocho, or Kiddush. In order to accomplish salvations and bring abundance of blessing to the world we have to fill ourselves up with Torah, this is the key thing. From here, we can thank Hashem for all the great things he was created in this world, and work on perceiving His omnipresence, like it says מלא כל הארץ כבודו, His honor fills the world. Once we accomplish this, our perception of physicality changes from that of dry and tasteless bread to that of tasty, oily bread, meaning that reality becomes full of delight and pleasure rather than depression and toil. After attaining this degree of perception, even if we have nothing we will have everything we need, since one who attains this realizes that Hashem never lets anyone lack, as everything is given according to their proper needs in accordance with the incomprehensible and wonderful Divine plan.
Yismach Lev 