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 ...
It seems that from what I've learned, the vast majority of Klal Yisroel didn't return for Beis Sheini. I was taught that this was on account of the fact that the talmidei chachamim didn't advocate the ...