[Background: The Ramban stated that the redemption of Ezra's time was only meant for the Jews of Babylonia, but Jews in other countries were still forbidden to violate the oath and ascend. Now the Rebbe will ask how it was permitted to live outside of Eretz Yisroel under idol worshippers when one could live in Eretz Yisroel under a Torah government. The Rebbe explained earlier (Siman 4-5) that the meaning of Chazal's statement that one who lives outside of Eretz Yisroel is as if he worships idols is because one is choosing to live under idol worshippers and pay taxes to them, rather than live under a Jewish Torah government. Therefore, he said, it does not apply during exile, where the idol worshippers are in control no matter where you go. Now he is pointing out that this leads to a difficulty explaining why Jews lived outside Eretz Yisroel during the Second Temple era.]
However, it is difficult to understand how, at the time of the Second Temple, when there was a Torah kingdom in Eretz Yisroel, and especially at the time of Ezra, it was permitted to live outside of Eretz Yisroel under an idolatrous government. Even according to my earlier explanation of why the statement "whoever lives outside Eretz Yisroel is as if he worshipped idols" doesn't apply nowadays, during the Second Temple period it certainly applied.
So we must say that the statement "whoever lives outside Eretz Yisroel..." refer only to one who leaves Eretz Yisroel of his own volition. [This was how Rabbi Yoshiahu Pinto explained it - see Siman 1 and Siman 4.] Although, as I pointed out, the Gemara's language "whoever lives" seems to include anyone living there, for whatever reason, later I looked at the source for this statement, the Tosefta of Avodah Zarah chapter 5. There it says, "Whoever leaves Eretz Yisroel in peacetime and goes out is as if he worshipped idols." So it states explicitly that it is only talking about one who leaves, and only during peacetime when there is nothing forcing him to leave. Similarly the Toras Kohanim (Parshas Behar) makes this statement explicitly about one who leaves, and the Shitah Mekubetzes on Kesubos actually had this in his text of the Gemara. [The Ramban in Sefer Hamitzvos seems to have had this text as well.]
Our version of the text could fit with that interpretation too, if we assume that the statement was made specifically to students in Eretz Yisroel. For them, the only way to live outside Eretz Yisroel was to leave it. We find the concept of a sage tailoring his teachings to students from different locations in Tosafos on Kiddushin 29b. There Rabbi Yochanan said, "When the millstone is on one's neck, how can he study Torah?" In other words, one should study Torah first and get married later, because after he gets married he will have to work and support his wife and he will have no time to study. Afterwards the Gemara, as explained by Tosafos, says that Rabbi Yochanan said this specifically to his students from Babylonia, because once married it would be impossible for them to leave home and come to study in his academy. So we see that although Rabbi Yochanan's statement was quoted without any qualifications, as it turns out it, it was only stated from the viewpoint of certain people. And we find similar things elsewhere in the Talmud. Here too, the statement "whoever lives outside Eretz Yisroel is as if he worshipped idols" was made to students living in Eretz Yisroel, and for them living outside Eretz Yisroel meant leaving Eretz Yisroel.
[However, this does not solve the Rebbe's other problem with Rabbi Yoshiahu Pinto's explanation, which he posed in Siman 4: how can we say that the statement about worshipping idols doesn't apply when one was forced out, if the source of this idea is the quote from King David, "For they have expelled me today from basking in the inheritance of Hashem, saying go worship other gods"? David was forced out, yet he was considered as if he worshipped idols!]
Accordingly, we understand why countless Tannaim and holy individuals lived in Babylonia and other countries outside of Eretz Yisroel even during the Second Temple era.
One might ask: it is written in certain books that Ezra the Scribe was angry at the Jewish communities of certain places for not returning to Eretz Yisroel, and his anger had a negative impact on them. [This may be a reference to the Seder Hadoros, 5380, who quotes the author of the Sma, Rabbi Yehoshua Falk Katz, as saying that the reason why there were so many destructions and pogroms in the city of Worms, Germany (notably the First Crusade in 1096, documented in Kinah 26 of Tisha B'av) was because the Jews came to Worms after the destruction of the First Temple, and after the 70 years of exile, the Jews of Babylonia returned, but the Jews of Worms did not. The Jews of Jerusalem sent a letter to the Jews of Worms inviting them to return and live in Eretz Yisroel, but the Jews of Worms replied, "You live in the great Jerusalem, and we will live in the little Jerusalem" - for they were treated well by their governor and had grown wealthy. Another possible story the Rebbe may be referring to is the one told by Rabbi Shlomo Adni, author of Meleches Shlomo on the Mishnah, in the introduction to his commentary. Rabbi Adni came from Yemen, and his family had a tradition that their ancestors had arrived in Yemen after the destruction of the First Temple. When the Second Temple was built, Ezra sent them a letter asking them to come, but they refused; Ezra cursed them that they should always live in poverty.]
However, perhaps there was a specific reason why Ezra called upon the Jews in those places to return, and he was angry at them for not listening to his call. But he was not upset with the vast majority of Jewish communities around the ancient world, or even with those who stayed in Babylonia – because that was how Divine Providence had arranged things. We will speak more about this later.
In any case, the Ramban's words are clear proof that he holds that the oath pertains even to immigration with permission, and even to a large group that is less than half of the Jewish people.