Why Can a Husband or Wife Can Force a Spouse to Move to Yerushalayim?

 Ha-Rav Shlomo Aviner, Nasi of Ateret Yerushalayim, once explained:

The Mishnah states: "A man or woman can force a spouse to move to Yerushalayim", such is the ruling when one spouse wants to live in Yerushalayim.  He or she has the upper hand, i.e. if the husband does not want to move there and they divorce, he must pay the Ketubah, and if the wife does not want to move there and they divorce, she is not paid the Ketubah (Ketubot 110b).  Yerushalayim is superior to all else, not in the sense of aloofness and arrogance, but in the sense of being the spiritual pinnacle of Eretz Yisrael.

But we can ask: We’ve heard over and over again about the Mitzvah of settling the Land, but where in the Torah is there a Mitzvah of settling Yerushalayim?  Answer: True, there is no special Mitzvah of settling Yerushalayim per se, but since it is the spiritual pinnacle of the entire land, the Mitzvah of settling the Land is all the more so fulfilled here.  David Ha-Melech states, “Hashem loves the gates of Zion more than all the dwellings of Yaakov” (Tehillim 87:2).  Obviously, this is referring to all of Yerushalayim, including the new neighborhoods of West Jerusalem.  Yet it is clear that the main thing is the Old City, Yerushalayim between the walls.

Perhaps this is the source of what I heard that one of the great sages of our generation, Ha-Gaon Ha-Rav Ahron Soloveitchik, was once asked: if a philanthropist wanted to donate a hundred million dollars to Torah institutions and he left the decision to you, where would you recommend?  He responded: To build Yerushalayim within the walls (from Ha-Rav Yaakov Marcus).