Would Halacha permit Eliyahu HaNavee (Elijah the Prophet) to come to herald the redemption on Shabbat?
The Gemara in Eruvin (43) addresses an interesting question regarding the prohibition of Techum Shabbat, which forbids traveling a certain distance outside one's city on Shabbat. The question is whether or not this prohibition applies when traveling in the air, above the height of ten Tefachim (handbreadths). One ramification of this issue addressed by the Gemara is whether Eliyahu HaNavee can come to us on Shabbat. Tradition teaches that Eliyahu will arrive on the day before the arrival of Mashiach, and that he will not come on Friday, so as not to interfere with people's Shabbat preparations. The Gemara remains uncertain, however, as to whether he can come on Shabbat, as this depends on whether the prohibition of Techum Shabbat applies to air travel. Since Eliyahu HaNavee will fly to us from the heavens, he will be permitted to come on Shabbat if the law of Techum Shabbat pertains only to land travel. If, however, the prohibition applies even to travel through the air, then Eliyahu will be unable to come to us on Shabbat. The Gemara does not reach a conclusion with regard to this issue.
The Chatam Sofer (Rabbi Moshe Sofer, Austria-Hungary, 1763-1840) asks why the Gemara did not resolve its question in light of the tradition that Eliyahu HaNavee attends every Brit Mila (circumcision ceremony). Presumably, he attends even Britot conducted on Shabbat, seemingly proving that he is permitted to fly from the heavens on Shabbat, which would lead us to conclude that Techum Shabbat does not apply to air travel. Why does the Gemara not mention this proof?
The Chatam Sofer answers that the Gemara discusses only Eliyahu's arrival in a physical form, as a human body. When Eliyahu comes to herald the redemption, he will arrive as a regular, physical human being, in which state he is bound by the laws of the Torah. Hence, the possibility of his arrival on Shabbat hinges on the issue of whether the Techum Shabbat prohibition applies to air travel. Eliyahu's attendance at Berit Mila ceremonies, by contrast, is only as a Neshama, as a spirit, and spirits are certainly not obligated to observe Halacha. Therefore, his arrival on Shabbat for a Berit Mila ceremony does not shed light on the issue of whether one violates Techum Shabbat by traveling through the air.
Conclusion: Eliyahu HaNavee cannot come on Friday, but the Gemara remains unsure as to whether he can come on Shabbat.
