The Gemara (Bab. Ber. 24b*) quotes R' Yehudah as saying that anyone who leaves Bavel to go to Israel violates an Isur 'Aseh (a violation of the parameters of a positive commandment), because the Navi says (Jer. 27:22), "They shall be brought to Babylon and there they shall [remain] until the day I redeem them."
Four(-ish) part question:
Why does the Navi have the power to enact a Biblical(-style?) law?
According to R' Yehudah, why was this still in effect in the times of the Talmud? After all, the Babylonian exile had ended and the Second Temple had been built by that time (and used for several hundred years, desecrated, re-dedicated, used for about 200 years more, and then destroyed again). Although R' Abba (and most Jews) lived in Bavel, this was the period of the Roman exile, which has lasted to today.
a. Did the Isur 'Aseh apply for all generations?
b. Does the Isur 'Aseh apply specifically because they went back to Bavel?
c. (If b.) Does the Isur 'Aseh apply only in Bavel?
(Closely related to 2a) According to R' Yehudah, would this apply even today? (Same sub-questions - does it apply only to Jews living in Iraq, or to everyone, and why?)
What about leaving Bavel to go somewhere else?
*Sorry, I'm behind on my Daf-Yomi Challenge questions!^
^(Others should feel free to participate!)
BTW, this should not get into Hashkafic considerations or political discussions with regard to positions held by Natorei Karta and/or other groups, although this may be the basis for their position. This question is purely exploring the Halachic reasoning of R' Yehudah as recorded in the Gemara.