The Torah Temimah (Parshat Re’eh ad loc.) questions this statement. Why should living in the Land of Israel be equivalent to all the other commandments? He suggests that it is impossible to fulfill all the mitzvot of the Torah except in Israel since there are a number of mitzvot whose performance is conditional on being in Israel. Thus, the Tosefta’s statement (that living in Israel is equivalent to all the mitzvot of the Torah) means that only in Israel is there the potential to perform all the commandments.
The Ramban, in his Mitzvot Asei (LeDa’at HaRamban), quoted in the first volume of the Rambam’s Mishneh Torah, lists settling in the Land of Israel as one of the positive precepts of the Torah. The Rambam, on the other hand, does not include it in his enumeration of the mitzvot asei.
The Ramban bases himself on Numbers 33:53 (Parshat Mas’ei): “Ve’horashtem et ha’aretz viyshavtem bah, ki lachem natati et ha’aretz lareshet otah – You shall inherit the land and dwell in it because I have given the land to you so that you inherit it.” The Ramban uses this verse as the source of the mitzvah rather than the verse in Parshat Re’eh that we quoted previously.
In his commentary to the verse in Parshat Mas’ei, Rashi notes that this verse teaches us that we should first inherit the Land of Israel from its occupants and then dwell in it. If we do so, then, and only then, will the Jewish people, be able to survive in the land. Thus, inheriting the land and actually living in it are intrinsically intertwined.
Ketubot 110b greatly expands on the Tosefta we cited earlier: “A person should at all times live in Israel even in a city where most of the inhabitants are idolaters, but one should not live outside the land even in a city where the majority are Jews because one who lives in Israel is considered as if he has a G-d and one who lives outside the land is compared to one who has no G-d, as it states in Parshat Behar (Leviticus 25:38), ‘Ani Hashem Elokeichem asher hotzeiti et’chem me’eretz mitzrayim latet lachem et eretz canaan lih’yot lachem l’Elokim – I am Hashem your G-d, who has taken you out of the land of Egypt to give you the land of Canaan, to be your G-d.’ ”
The Gemara’s assumption is that upon entering and settling Israel one automatically acknowledges G-d, and conversely, one who does not live in Israel does not automatically acknowledge G-d (and thus may be compared to an idolater).
In this light, continues the Gemara, we may also read the statement by David made before King Saul (I Samuel 26:19): “Ki gershuni hayom mehistape’ach benachalat Hashem leimor, lech avod elohim acherim – For they have chased me away this day from joining the inheritance of G-d, saying, ‘Go serve other gods.’ ” (Indeed, we find in I Samuel [infra chap. 27] that David flees to the land of the Philistines which, though it was part of the land promised by G-d to Abraham, was nevertheless inhabited by the Philistines and, for all practical purposes, sojourning there was akin to sojourning outside the land of Israel.)
The Gemara observes that we are not informed that anyone told David to worship other gods; therefore, he must be teaching us that living outside the land is like worshiping idols.
The Maharsha asks what the meaning of this Gemara is. He notes that Hashem is surely the G-d of the whole world. How does living outside Israel make one an idol worshipper? Although Hashem is referred to as “the G-d of the Land” – meaning the land of Israel – one who lives outside Israel cannot be referred to as being without a G-d since Hashem is the G-d of the whole world.
What the Gemara means, rather, is that someone living outside of Israel is considered like an idolater who does not accept Hashem as his G-d – just like the nations of the many lands who worship idols. This was what David meant when he said that he was told to serve other gods; Saul had forced him to live outside Israel, in a place of idolatry.