Reviving the Heart Through Learning Maseches Sukkah:
Almost every year, the Koloshitzer Rebbe zy"a would relate the following story on Motzoei Yom Kippur in the name of his grandfather, the Sanzer Rov zy"a:
After his marriage, the Yeshuos Yaakov zt'l was supported by his mother-in-law in the city of Yaroslav. One year, the Yidden of that city went to shul for Kol Nidrei on the eve of Yom Kippur, and they saw a man with a nice beard and shining face standing before the amud. He began Kol Nidrei and chanted the words with extreme enthusiasm, as the entire congregation recited the prayer along with him. They also allowed him to serve as the chazan for Maariv, as they saw that he was a holy man.
This was Rav Levi Yitzchok of Berditchov zy"a. His tremendous hislahavus and kedusha cast a shadow of fear upon the people. Everyone sitting on the Mizrach wall moved towards the back because they were afraid to look at his fiery face.
After Maariv, everyone went home. When they came back in the morning, they saw that the Berditchover was again still by the amud. He had not moved from that place all night. He proceeded to serve as the chazan for all the tefillos – Pesukei D'Zimrah, Shacharis, Mussaf, Minchah and Neilah.
After Maariv, as Yom Kippur ended, everyone wanted the zechus of inviting him to their house to break his fast. They understood that he had come to raise funds for some worthy cause, so they decided that whoever pledged the most money would host him for the seudah. They began to place their bids, with the amount growing higher and higher.
The Yeshuos Yaakov's mother-in-law was sitting in the Ezras Nashim, wearing a necklace bedecked with exquisite gems. She immediately took it off and threw it into the bais medrash as a donation to the guest. Since the necklace was worth more than all the bids, she merited hosting Rav Levi Yitzchok.
Rav Levi Yitzchok walked to her home, accompanied by the Yeshuos Yaakov, and made Havdalah. The mother-in-law put all kinds of delicacies on the table, but the Berditchover screamed, "I need something right now to revive my heart."
The Yeshuos Yaakov understood what he meant. He brought him a Gemara Maseches Sukkah, and the Berditchover sat down and learned from it all night, finishing the Masechta with Rashi and Tosafos by morning.
The Sanzer Rov would conclude by saying, "There are many difficult Tosafosim in Maseches Sukkah. Learning this Masechta is what revived his heart."
Learning Maseches Sukkah Saves From Harm:
The Tosher Rebbe zy"a writes (in Sefer Avodas Avodah, Sichos Kodesh, Chelek, page 381) that his grandfather, Rav Elimelech of Tosh zy"a showed him a maamer that says: "Anyone who learns Maseches Sukkah will be saved from all suffering and danger."
Rav Elimelech would say that Maseches Sukkah was his "Maseches Olam Haba", and he would learn it many times through the year with much iyun.
On this topic, the Munkatcher Rov zy"a writes (Divrei Torah, Mahadura 7, Ois 49): "I heard in the name of the gaonim and tzadikim of Ashkenaz z"l that it is a segulah to learn Maseches Sukkah every day. Through doing this, our enemies will fall and become subjugated, and will be unable to do us any harm."
He adds that there is a hint to this in the pasuk in Tehillim (31:21): "You shall hide them in the shelter of Your face, from bands of men; protect them in a sukkah from the strife of tongues." The pasuk can be understood as saying that when one "hides in the shelter" of the sukkah, by learning Maseches Sukkah, he will be saved from "the strife of the tongues" of prosecuting forces and enemies that wish to harm him.
This is also hinted to by the words: "Vayomer Hashem salachti k'devarecha." (And Hashem said, "I will forgive them like your word.") The first letters of these words spell the word "Sukkah".