In Parshas Vayakhel the Torah continues detailing the building of the Mishkan and its vessels, and the kohanim’s garments. Rabbeinu Bachya points out that of all the materials that were donated to the building of the Mishkan, we do not find the inclusion of meshi (silk). His reason: because it is made from a worm, and only material that came from items that were tahor and were permitted to be consumed were used in the Mishkan.
Regarding this, the Acharonim say that even though techeiles comes from a non-kosher worm – the cheilazon – it was used in the Mishkan. There is a dispute, however, as to the kashrus of the cheilazon. Rashi, in Sanhedrin 91, says that the cheilazon was a worm from the sea, implying that it was not kosher. But the Radziner Rebbe, in Pesil Techeiles, writes that the Cheida says that the cheilazon was a kosher fish. Similarly, the Rambam (Hilchos Tzitzis 2:2) says that the cheilazon was a fish. This seems to contradict Rashi’s explanation of the cheilazon. The Noda B’Yehudah also says that according to the Rambam the cheilazon was in fact a kosher fish.
According to the latter opinion, it is obvious that the question of how techeiles was permitted in the Mishkan is a non-starter. Nonetheless, according to the opinion that holds that the cheilazon was a worm, we need to understand how it was permitted to be used in the Mishkan.
The Cheida (Nachal Kedumim, Parshas Terumah) says that according to those who opine that the cheilazon was a non-kosher fish, the reason it could be used in the Mishkan was because it was mixed with other ingredients. With this being so, we apply the halacha of zeh v’zeh goreim – when two things make a joint contribution, we allow the forbidden item (see Sanhedrin 80a).
The Radziner Rebbe cites several Rishonim who hold that one may eat the blood of a non-kosher fish. Only the flesh of the fish is prohibited to consume; the blood is permitted mi’de’oraisa. Since the techeiles dye is produced from the blood of the cheilazon fish, it would be a permitted material in the Mishkan.
The opposite was also true. The Gemara (Shabbos 108) says that tefillin may only be made from items that are permitted to be consumed; the hide must be from a kosher animal. The Gemara there says that if a kosher animal dies without shechitah and is now forbidden to be eaten (as it is a neveilah), its hide may still be used to make tefillin because the animal’s species are kosher.
Additionally, the Chasam Sofer (Teshuvos Orach Chaim 39) writes that many people use the gid hanasheh to bind Sifrei Torah, tefillin, and mezuzos even though gid hanasheh may not be eaten. Why? Because it comes from a kosher species. Therefore, even if the item that is being used cannot be eaten in its current state, it may be used if it is of a kosher species.
The Chasam Sofer’s proof regarding those who hold that the gid hanasheh may be used for tefillin is that the hides of eilim m’adamim were used in the Mishkan. These hides, dyed in blood, were forbidden to be eaten. Yet since the blood came from a species of animal that was kosher, its blood was permitted to be used with the materials of the Mishkan. The Chasam Sofer nevertheless adds that his rebbe, Rav Nosson Adler, opposed the allowance of the gid hanasheh to be used in binding Sifrei Torah, tefillin, and mezuzos.
The Mishnah Berurah (32:24) cites Acharonim who, disagreeing with the Chasam Sofer’s decision, prohibit the use of the gid hanasheh in binding Sifrei Torah, tefillin and mezuzos. Rav Chaim Kanievsky, shlita, writes in Maseches Sefer Torah that the basis of this opinion is that although the item may be unfit for consumption in its present state, as is evident from the aforementioned Gemara in Shabbos concerning neveilos of kosher animals, the item was at one time permitted to be eaten – namely, before they became neveilos. The gid hanasheh, on the other hand, was never permitted to be eaten.