“And Yisro rejoiced over all of the good that G-d did for Israel” (Sh’mos 18:9). In the Mechilta (quoted by Midrash HaGadol), Rabbi Eliezer describes the “good” that Yisro was told applies to the Children of Israel: “They said to him, ‘G-d is going to give us the Land of Israel, the World to Come, a New World, the Kingship of the House of David, Kehuna and Leviya.” Rav Yitzchok Sorotzkin, sh’lita (Rinas Yitzchok al HaTorah I) asks how the World to Come could be included with the good that is designated for Israel if righteous gentiles merit the World to Come as well (see Rambam, Hilchos T’shuvah 3:5 and Hilchos M’lachim 8:11). He then points us to what he wrote in his commentary on Rambam’s Hilchos T’shuva and his commentary on Rus (2:12) for further discussion.
In his commentary on Rus he quotes a similar question asked by Rav Meir Soloveichik, sh’lita, as elsewhere (Hilchos Isuray Biya 14:4) Rambam says that the World to Come is “hidden” (or “waiting”) only for members of the Jewish nation. How can this be reconciled with Rambam stating elsewhere that gentiles can merit the World to Come? This question can, IMO, be answered rather easily, as from the context (as well as from the continuation of the Talmudic statement that Rambam is based on) it seems that Rambam is not discussing who is able to merit a share in the World to Come. Rather, it is the kind of share received in the World to Come, and how that share is affected by the amount of suffering the individual experienced in this world. Rambam’s point is that the bulk of a person’s reward and punishment is not given in this world, but is “waiting” for the next world (where everything ultimately is balanced out). This aspect, though, only applies to Jews, even if non-Jews can merit a share in the next world. Nevertheless, even if this would explain Rambam’s view, it would not explain how Yisro could be told that meriting the World to Come is something reserved only for Israel.
In order to answer the question posed by Rav Soloveichik, Rav Sorotzkin quotes the Talmud (B’rachos 34b), where Rabbi Yochanan is quoted as saying that all of the prophecies stated regarding the World to Come can only be about the share merited by those who have repented after sinning (or are in the process of repenting); the World to Come merited by the completely righteous, on the other hand, cannot be seen/understood by the human eye/mind. Although Rambam (Hilchos T’shuva 7:4) quotes the opinion that (the Talmud says) argues with Rabbi Yochanan (as it seems to be saying that those who have sinned and repented are on a higher level than those who never sinned), Rav Sorotzkin suggests that the two types of “Worlds to Come” described by Rabbi Yochanan (see Maharsha) can be applied to different worlds awaiting the righteous Jew and the righteous gentile. If so, Yisro could have been reacting to the higher-level World to Come that awaits members of the Nation of Israel. [For further discussion on possible differences between the World to Come awaiting righteous Jews and the World to Come awaiting righteous gentiles, see Ramchal, Derech HaShem 2:4:7 and Tiferes Yisroel, Sanhedrin 10:2, although the latter’s approach is difficult to fit within the context of the Mishnayos that limit which Jews get a share in the World to Come.]
In his commentary on Rambam’s Hilchos T’shuva (G’vuras Yitzchok, Yomim Nora’im), Rav Sorotzkin also tries to reconcile Rambam’s saying in one place that righteous gentiles can merit a place in the world to come while indicating elsewhere that it is only for Jews. First he quotes Sefer Ha’Ikarim (4:30) regarding Rambam’s position that there are two kinds of “worlds to come,” one referring to after the resurrection of the dead and the other where only the soul exists. [Actually, there would be three or four stages; after death but before the body decomposes, after the body decomposes, after the resurrection of the dead, and then, according to some, the ultimate existence after that. Obviously, no one knows for sure about the nature of life after death; even though my grandfather, a”h, promised me that after 120 years he would tell me what it was like on the other side (and he did), that could only be about what things are like after death, not what happens regarding the resurrection of the dead, etc.] Similarly, Rav Sorotzkin references Ramban’s position in Sefer HaG’mul that there is more than one “paradise” (“Gan Eden”), one while the soul is still somewhat connected to the physical world and one after the soul has completely disconnected from it. If there is more than one type of “Worlds to Come,” Rav Sorotzkin continues, but not all of them can be merited by righteous gentiles, Rambam could be referring to one type when he says that they can gain a share in the World to Come while referring to another when he indicates that it is only for Jews. However, Rambam’s wording (Hilchos T’shuvah 3:5) indicates that he was referring to the same “World to Come” for both.
Rav Sorotzkin also quotes Tiferes Yisroel’s question on the Mishnah in Sanhedrin, where he asks how the Mishnah can imply that only Jews have a share in the World to Come if righteous gentiles can as well. To answer this question, Rav Sorotzkin points out that except for the listed exclusions (such as being a heretic), all Jews have a share in the World to Come, even if they are wicked (which is the straight-forward reading of the Mishnah, and is explicit in Rambam’s words in Hilchos T’shuvah), whereas only righteous gentiles merit a share in the World to Come. It should be noted that when Rambam elaborates on what it means to be a “righteous gentile” (thereby qualifying for a share in the World to Come), he explains that it is someone who has accepted the obligation to keep the seven Noachide laws, and keeps them because G-d commanded him or her to do so. This definition leaves little room for someone to meet the qualifications yet be considered “wicked.” Still, the exceptions he lists for Jews (Hilchos T’shuvah 3:6-14) don’t leave much room for being wicked either, so it’s difficult to pin anything on a difference in the ability to be considered “wicked” while fulfilling the requirements necessary to merit a share in the World to Come. Nevertheless, since the starting point for (religious) Jews is having a share, whereas the starting point for gentiles is having to earn a share (a difference based mostly on the starting point of how each was raised), this could theoretically explain the “good” Yisro rejoiced over.
Looking at the list of how one can lose their share in the World to Come, it becomes clear that being part of the Jewish people is the starting point to having an automatic share, while becoming disconnected from the nation is how one loses that share. (This doesn’t preclude the possibility that one who has lost his or her share because they removed themselves from the collective can still earn a share in other ways. The “share” we start with is because we are part of the collective; we can earn a greater share by making additional connections with the Creator. That our share in the World to Come is based on the connection we make with G-d is evident from the fact that gentiles fulfilling the Noachide laws only merit the World to Come if they are doing so because G-d commanded it; this concept would apply to Jews as well.) As a unit, we help each other develop a stronger relationship with G-d, whether by building Houses of Worship and Houses of Study, by creating a market that makes keeping kosher (et al) much easier, or merely by being part of a culture that fosters spiritual growth. Every member of our “community” helps other individuals earn their share in the World to Come (at least to some extent), and therefore gets credit for doing so. Because we each contribute to others gaining a share in the World to Come, we automatically get to partake in it as well (besides being able to earn shares in our own right). As long as one has not removed him or herself from the community, merely being part of the community qualifies as being “righteous,” and therefore merits getting a share in the World to Come. (A similar concept may work for a community of Noachides, but they must build their own community; we had the foundation for our community built for us in the merit of our Patriarchs and Matriarchs.)
When Yisro heard about “all that G-d had done for Israel,” it referred to the structural foundation that would allow us to become “a kingdom of priests and a holy nation.” Rabbi Eliezer (in the Mechilta) listed the specifics of that foundation: a land suited for spiritual growth that we can call our own; the ability to build a “new world,” i.e. a society that would be like no other; a righteous government that would oversee this society to ensure that it followed G-d’s guidelines; a family designated for Temple service that wouldn’t be distracted by having to work the land for survival; and a Tribe similarly designated to support them and to teach others how to live their lives properly. Included in this “good” was the culture that was being created that not only made it easier to merit the World to Come, but bestowed upon each member of the nation a share in that world just for being a supporting member of that culture. This aspect only applies to our nation, and when Yisro understood how beneficial this system was for every individual who was part of it, he rejoiced.