(Background: the Rebbe is discussing the opinion of Rav Yehuda in Kesubos 110b that even individual Jews are forbidden to go to Eretz Yisroel. Rav Yehuda seems to conflict with the Mishnah, which says that husbands and wives can force each other to move to Eretz Yisroel or not to leave it.)
However, in my humble opinion this is not a problem at all, for Rabbi Meir of Rothenberg (quoted by the Rosh in siman 17 of this chapter of Kesubos) has already established that our Mishnah only applies during the times of the Temple. Rabbi Meir of Rothenberg is dealing with the Jerusalem Talmud, which says that only the husband may force his wife to move to Eretz Yisroel, but the wife may not force her husband. How, he asks, is this consistent with our Mishnah? He answers that the Mishnah applies in Temple times, but nowadays only the husband may force his wife.
The Beis Shmuel (Even Hoezer 75:20) rules in accordance with the opinion of Rabbi Meir of Rothenberg. But the Chasam Sofer (Yoreh Deah 234) disagrees, based on Gittin 45a, where the Gemara says that if a slave flees from his master to Eretz Yisroel, his master must set him free. The Gemara bases this rule on the Mishnah in Kesubos 110b: “No one may force another to leave Eretz Yisroel,” and also on the verse, “You shall not return a slave to his master.” Now, what is the proof from the Mishnah? The Mishnah only applies in Temple times, but nowadays, a slave is no better than a woman, who cannot force her husband to move to Eretz Yisroel! So it seems that the Babylonian Talmud held that the Mishnah applies nowadays as well. And even Rabbi Meir of Rothenberg only meant to explain the Jerusalem Talmud, not to imply that our Talmud – the Babylonian – also holds this way.
In my humble opinion, the Beis Shmuel would answer that there is a difference between the law of the slave who wishes to move to Eretz Yisroel and the law of the wife who wishes to move to Eretz Yisroel. The law of the slave is derived from the verse, “You shall not return a slave to his master,” which the Rambam and others count as one of the 613 Commandments. We do not look at the reason for the commandments, so this law applies at all times, even after the destruction of the Temple. The law of the wife, on the other hand, is a Rabbinic enactment based on the fact that it is a mitzvah to live in Eretz Yisroel – a mitzvah regarding which there are many disagreements and distinctions, depending on the circumstances, as I will explain, G-d willing, in Maamar Sheni.
That there is a difference between the slave and the wife is clear from the Responsa of the Ran, siman 38, who understands that the entire issue of forcing a spouse was only said regarding a divorced couple who are fighting over the kesuba, but when they are married, neither can force the other to move. This is clearly different from the slave, who can actually force his master to move to Eretz Yisroel or else set him free.
The other poskim disagree with the Ran and hold that one may force a spouse to move while married to him or her. But the foundation of this law is not a Torah law; rather the idea is that if he moves to Eretz Yisroel and she refuses to come along, she has the status of a “moredes” (a wife who refuses to have marital relations with her husband) – see Beis Shmuel 75:2. Now, the entire law of a moredes is a Rabbinic enactment, because in the eyes of the Torah, as long as they are married, they are obligated to one another. In the eyes of the Torah, the husband must support even if she refuses to come with him. So this is not similar to a slave who ran away to Eretz Yisroel, who goes out free by Torah law, based on the verse “You shall not return a slave to his master.” This is not a law that he may demand his freedom (like a wife who moves to Eretz Yisroel, who may demand a get). Rather, he is automatically free. According to the Ri (Rabbeinu Yitzchok of Tosafos) he is free already and he lacks only the document of freedom (which permits him to marry a Jewish woman). According to the Rambam, if the master refuses to free him the court may free him. This is explicit in the Gemara (Gittin 45a), and this is how the Beis Yosef rules in Yoreh Deah, end of 267.
One might be misled and think that the law of the slave is part of the same Rabbinic enactment as the law of the wife, based on the fact that the Gemara says, “No one can force the other to leave Eretz Yisroel – this comes to include a slave who ran away to Eretz Yisroel.” But this is not the case – the law of the slave is based on an explicit negative commandment. Rather, it is normal for a Mishnah to use all-inclusive words (such as hakol – “everyone” or “no one”) to allude to a similar law, even when the other law is based on a totally different reason. This occurs in many places in the Talmud. And here the laws of the slave and wife are especially similar since the Mishnah is talking in the times of the Temple, according to Rabbi Meir of Rothenberg, and at that time the law of the wife was equal to the law of the slave: she had the right to force her husband to come to Eretz Yisroel or divorce her, just as a slave has the right to force his master to move to Eretz Yisroel or free him. But it may very well be that after the time period discussed in the Mishnah the situation changed, such that the wife’s law is different from the slave’s.
In conclusion, we see that Mishnah about the husband and wife forcing each other is talking only in the time of the Temple.