The obligation to separate terumot and ma'aserot in Jerusalem and throughout Israel today
Is the obligation to separate terumot and ma'aserot rabbinic or biblical in today's day and age? What are the implications of Jewish demographics on this obligation, and what does the Rambam have to say on the matter?
The Rishonim disagree whether the obligation of taking terumot and ma'aserot (T&M) today is biblical or rabbinic in nature. Some maintain that the second measure of sanctity that Ezra and olei Bavel (kedusha shniyah) imbued in the areas they returned to in the Land of Israel was not nullified upon the Second Temple's destruction and exile from the Land of Israel. According to this opinion, T&M would be a biblical injunction. Others believe, however, that this sanctity was voided, and that today T&M is a rabbinic injunction.
In this way many Rishonim link the sanctity of the Land of Israel today and the level of obligation of separating T&M. The Rambam, though, does not link the two, and has an innovative approach to the topic. According to the Rambam, despite the fact that the sanctity of Ezra continues to exist and was not nullified upon the destruction of the Land of Israel and the subsequent exile, he rules that this is still insufficient grounds to obligate T&M from the Torah. The Rambam's reasoning is that when Ezra returned to the Land of Israel, not all (or most) of the Jewish people made Aliya with him; the condition for a biblical obligation being "bi'at kulechem" ("when you [all] come", a reference to bevo'achem, "in your coming," Bamidbar 15:18).
The Rambam's super-commentators were divided in their understanding this deficiency, whether or not this is an integral deficiency relating to the sanctity of the Land of Israel. One approach is that in order for the sanctity of the Land of Israel to apply in full, at the time of sanctification process most of the Jewish people need to be living there. If this is true, since most Jews lived abroad in Ezra's time, the Land's sanctity will not return without an additional sanctification process.
Another approach to the Rambam is that the obligation of separating T&M is linked to the situation at hand. That is, the biblical obligation of T&M applies only when the majority of the Jewish People are in the Land of Israel. According to this understanding, the moment that the majority of the world's Jewish population lives in Israel, separating T&M becomes a biblical obligation, without a need for an additional sanctification process.
An additional practical implication of this issue is the obligation of separating T&M in Jerusalem and the Temple mount today. These areas, according to the Rambam, were imbued with sanctity from the time of Yehoshua and olei Mitzrayim. Some maintain that since at that time the vast majority of Jews lived in the Land of Israel, the obligation is currently biblical, even if today the majority does not live in Israel. Others, though, view "bi'at kulechem" as a standing condition for obligating of separating T&M . It follows that since there were times when most of the Jews did not live in the Land of Israel, the obligation of separating T&M in Jerusalem is only rabbinic.
In practice
Some interpret the Rambam to say that the moment the majority of the Jewish population resides in the Land of Israel (which will probably occur in the next few years), separating T&M throughout Israel becomes a biblical obligation, even without an additional sanctification process. Others read into the Rambam that separating T&M in Jerusalem's Old City is a biblical obligation, while other halachic opinions view this mitzvah as rabbinic in nature.
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