Hoshana Rabba
Hoshana Rabba
Sources from Yerushalmi through the Rishonim identify Hoshana Rabbah, not only Yom Kippur, as a day of sealing the year's gzar din, tied especially to the judgment on water and the closing of the aravah and nisuch hamayim. Because the day carries this weight, the minhagim matter: staying up after chatzos to say the entire Tehillim plus Chumash Devarim and passages of Zohar, coming to daven and say all the hoshanos, and eating a full Yom Tov seudah rather than treating the day as ordinary. Skipping the seudah in particular reads as a lack of confidence that a gutte kvitel is coming.
Hoshana Rabba
While Yom Kippur is popularly known as the day of the final seal, the Zohar places the true gmar chasima — the 'gutte kvitlach' — on Hoshana Rabbah instead, which is why an all-night Tehillim and a full seudas Yom Tov are kept with the same seriousness as Rosh Hashanah and Yom Kippur. A further point is built on the name itself: 'gadol' or 'rabbah' can only be an absolute description, not a relative one, when it refers to something infinite, so Hoshana Rabbah, the day of many hoshanos, is really the day capable of drawing down boundless yeshuos, culminating in the ultimate yeshuah of the geulah.