Two Days of Yom Kippur
A valid question which I am sure not many people are asking, for obvious reasons, is why don’t Jews outside of Israel observe two days of Yom Kippur. We already known that in the Talmud the question was discussed and Ravah was known to observe two days of Yom Kippur (see bRosh HaShannah 21a), but what about everyone else. Considering the amount of difficulty which many people have with fasting one day, it is not surprising that two days of Yom Kippur never caught on. While this may be true for the majority of Jews, during the Medieval Period there definitely were some Jews, it is not clear how many, who took it upon themselves to observe Yom Kippur for two days.
There is a tradition found in numerous collections from the “School of Rashi” about two sages, R. Yitzhak HaLevi and R. Yehuda b. R. Baruch (there are variations as to the exact names) who fasted on Yom Kippur for two days (see Sefer HaPardes p. 234; Siddur Rashi par. 204; Mahzor Vitry, p. 381 in the Horowitz ed.; Sefer HaRavyah par. 886, p. 659). Both of these rabbis were scholars from Worms and Mainz, and were students of Rabbeinu Gershom Meor Hagolah (“the Light of the Exile”) and at least R. Yitzhak HaLevi is known to have been a teacher of Rashi (see Aptowitzer, Mavo Sefer haRavyah, p. 367). Also see the R. Isaac of Vienna’s Or Zarua where he says that he wouldn’t think too highly of those who observed Yom Kippur for two days, since it was in his eyes dangerous, until he saw his teacher R. Judah the Pious, R. Yehudah HeHasid, and the Ravyah himself observe it for two days (Or Zarua, vol. 2, par. 281).
Gemar Hatimah Tovah.
Sources: Encyclopedia Talmudit, vol. 22, column 565 and note 2190; Avraham Grossman, Hachmei Ashkenaz HaRishonim, p. 287, see note 117.