The first mention of any significance to the seventh day of Sukkot is from the Mishnah (Sukkot, 4:5), which records that in the time of the Bet ha-Mikdash, the people would circle the altar seven times on this day. However, the Mishnah did not record any special name to the day or explain the significance of these seven circles, see our discussion, "Aravot in the Bet ha-Mikdash."
The Talmud Yerushalmi (Rosh Hashanah, 4:8) derives from Yishayahu 58:2 that there is a connection between the shofar and the aravot, and the reference to aravot most likely refers to the beating of the willow on the seventh day of Sukkot, which today we do after reciting the hoshanot prayers, see our discussion, "Beating the willows." This passage suggests a special significance to the seventh day of Sukkot in the Talmudic period, but nothing is spelled out.
The Talmud Yerushalmi (Rosh Hashanah, 4:8) derives from Yishayahu 58:2 that there is a connection between the shofar and the aravot, and the reference to aravot most likely refers to the beating of the willow on the seventh day of Sukkot, which today we do after reciting the hoshanot prayers, see our discussion, "Beating the willows." This passage suggests a special significance to the seventh day of Sukkot in the Talmudic period, but nothing is spelled out.
In the times of the Geonim, Rav Saadiah Gaon (10th century) and Rav Hai Gaon (11th century) write that the custom was for people to circle seven times in the synagogues on the seventh day of Sukkot. It is also recorded that Rav Hai Gaon would go to Jerusalem and circle around the Mount of Olives, seven times on the seventh day of Sukkot (Zevin, 1956, pp. 124,125).
A little after the time of Rav Hai Gaon, Rashi (1040-1105, commentary on Yuma, 21b) refers to the seventh day of Sukkot as the day of completion of the judgment on the water. This accords with the idea of the Mishnah (Rosh Hashanah 1:2), that on Sukkot, G-d judges how much water there will be for the coming year, and the idea of completion refers to the seventh day as being the last day of Sukkot.
Around this time or a little afterwards, the term Hoshana Rabbah was coined, most likely due to the practice to recite piyyutim with the word Hoshana many times, rabbah, when people would circle the bimah (bamah) in the synagogue seven times. This name is found in the Manhig, 1155-1215, Laws of Etrog 38, and Midrash Tehillim, 11th century?, on Psalm 17, see Elbogin, 1972, p. 420, footnote 33, and Zevin, 1956, p. 124.
Apparently also around the 12th century, the prayers on Hoshana Rabbah were increased by reciting some of the prayers for Shabbat/ Yom Tov on Hoshana Rabbah, Machzor Vitry, quoted by Elbogen, p. 105. These additions are adding mizmoring (chapters) from Tehillim, the piyyut nishmat at the end of pesukei de-zimra and an expanded kedusha by Musaf. The Darkei Moshe (Orah Chayyim 664) quotes from R. Yitzhak Tyrnau (late 15th century) that on Hoshana Rabbah we do not recite nishmat and we do recite the chapter 100 in Tehillim, mizmor letodah, which indicates that the day is a regular weekday and not a special day, though R. Yitzhak Tyrnau also said to recite extra short prayers when taking the Sefer Torah out of the aron kodesh as we do on Shabbat/ festivals. These additions do not include the reciting of the 13 attributes of G-d, which we recite today on Hoshana Rabbah, since mentioning the 13 attributes of G-d when taking the Sefer Torah from the aron kodesh was only introduced into the Siddur on any occasion in the 17th century by Natan of Hanover (Millgram, 1971, p. 497). These additions to Shacharit on Hoshana Rabbah in the Middle Ages also do not include reciting Tehillim chapter 130, shir hamalot mimakim right before barkhu in Shacharit, which today we recite on Hoshana Rabbah, since this chapter seems only to have begun to be recited in the ten days of repentance in the late 16th century.
Zevin (p. 126) also quotes that in a footnote to the Shibolei Haleket (Zedekiah ben Abraham Anaw, 13th century, Rome) it is recorded that some communities recited the additions that we make to the Shemoneh Esrei during the ten days of repentance and Avinu Malkenu on Hoshana Rabbah, but we do not do follow this practice.
The next stage in the development of Hoshana Rabbah was that it went from being a day of judgment of water to being a day of judgment of people. It is not clear when this development occurred.
Zevin (1956, p. 126) writes that this is from the Zohar (Tzav, 3:31b) which develops the idea of the judgment being on Yom Kippur, but that the decree, "the papers," are sent out on the seventh day of Sukkot. This development contradicts the discussion in the Talmud (Rosh Hashanah 16a) that a person's fate is sealed on Yom Kippur and all our prayers on Yom Kippur that are based on this idea, as for example, Unetanneh tokef and Neilah. Also, this idea of sending out "the papers" with the judgment seems incredible in reference to G-d.
While this is a delicate subject since it relates to the question when was the Zohar written (my understanding is around the 13th century), my guess is that the idea that Hoshana Rabbah was a final, final day of judgement was pre-Zohar, which the Zohar incorporated and maybe refined.
This understanding is because we see two customs on Hoshana Rabbah which indicate that the day was a day of judgment of people and the customs seem to predate the Zohar. One custom was the strange custom of a person going out with just a robe (toga?) on the night of Hoshana Rabbah, and then disrobing (in a secluded place?) to see his/ her shadow in the moonlight. The idea was that by seeing or not seeing the shadow a person could tell if he/ she would live and/or other ominous events in the coming year. Trachtenberg (2004, p. 215) writes that the first Jewish reference for this custom is from the Rokeah, R. Eliezer of Worms, 1176-1228, and it is briefly referred to in the Ramban's commentary on Bemidbar 14:9. (For more on this custom, see Abduraham, 14th century, Laws of Sukkah, the Rama, 16th century, in the Darkei Moshe, Orah Chayyim, 664, and on the Shulchan Arukh, 664:1, and Sperber 1990, pp. 15,16, and 1998, pp. 173-182. Note, the Abduraham and the Rama advice people not to do this custom.)
A second custom which also pre-dates the Zohar and indicates that Hoshana Rabbah was viewed as a day of judgement is that the Manhig noted that in France people would like candles on Hoshana Rabbah like they did on Yom Kippur, quoted by Zevin, p. 126. The idea of these candles was that if they did not go out on Yom Kippur or Hoshana Rabbah, then they were also supposed to show that a person would survive the year, see Trachtenberg (2004, p. 214), and comments of the Rama on Orah Chayyim 610:4 by the candles on Yom Kippur. The Tur (14th century, Orah Chayyim 664), which is not a Kabbalistic work, mentions this custom of lighting the candles on Hoshana Rabbah like by Yom Kippur. Similarly, the Shulchan Arukh (16th century, Orah Chayyim 664:1), which is influenced by the Kabbalah, mentions that people are to lite candles on Hoshana Rabbah like by Yom Kippur. I do not think that anybody does either of these customs today, but they indicate that Hoshana Rabbah was considered a day of judgment amongst Ashkenazim in the early Middle Ages seemingly prior and independent of Kabbalistic beliefs.
Other customs which relate to Hoshana Rabbah being viewed as a day of judgement but are apparently from the late Middle Ages since they are not quoted by the Tur but they are quoted by the Rama (664:1) are for people to go to the mikvah before dawn on Hoshana Rabbah and that some people, not just the chazzan as we do today, would wear a kittel (white robe) on Hoshana Rabbah as people do on Yom Kippur.
The next stage in the development of the seventh day of Sukkot was that many prayers were added relating to water, see Tur Orah Chayyim 664. On Hoshana Rabbah, we first circle around the bimah (bamah) seven times, and by each circle, we recite a piyyut, altogether seven piyyutim, based on the phrase “anna G-d hoshiah na.” Afterwards, we recite another seven piyyutim, some of whom are prayers for rain, after we return to our places in the synagogue. After reciting the two sets of seven piyyutim an extra piyyut kol mevasser is added, and we beat the willows. The piyyut kol mevasser is a prayer for the messiah to come. It is possible that this messianic piyyut was added by the people who were expelled from Spain or their descendants since this tragedy generated a fervent messianic belief.
The Kabbalists of Sefat (16th century), many of whom were expelled from Spain or were the descendants of people expelled, seem to have added another element to Hoshana Rabbah, the custom of having a tikkun on the night of Hoshana Rabbah. Abuduraham mentions a custom to learn on the night of Hoshana Rabbah in order for a person to read all of the Torah twice and the Targum once, as the reading of the Torah was about to be completed on Simhat Torah. Abuduraham thinks this is too much to do in one night and advices people to do this learning on the ten days of repentance. It is not clear if the Kabbalists in Sefat were influenced by Abuduraham's comments, but they developed their own customs as to what texts to study on the night of Hoshana Rabbah, see Faierstein, 2012, and our discussion, "Tikkun leil Shavuot."
With all of these developments, Hoshana Rabbah has become a special day, more significant than the other days of chol ha-moed Sukkot.
Bibliography:
Elbogen, Ismar (1874-1943), 1972, Prayers in Israel, Hebrew, Tel Aviv: Dvir.
Faierstein, Morris M., 2012,Tikkun Leil Hoshana Rabbah, Conservative Judaism, 63:4 Number 4, pp. 92-95.
Millgram, Abraham, 1971, Jewish Worship, Philadelphia: The Jewish Publication Society.
Sperber, Daniel, 1990 (vol. 1), 1991 (vol. 2), 1995 (vol. 3), 1995a (vol. 4), 1995b (vol. 5), 1998 (vol. 6), 2003 (vol. 7), 2007 (vol. 8), Minhagei Yisrael: Sources and history, Jerusalem: Mossad Harav Kook.
Trachtenberg, Joshua (1904-1959), 2004 (re-print of 1939 edition), Jewish magic and superstition: A study in folk religion, Jerusalem: Sefer ve-Sefed Publishing.
Zevin, Shlomo Yosef (1890-1978), 1944, first edition, 1956, seventh edition, Ha-Mo'adim ba- Halakhah, Jerusalem.