1) THE OBLIGATION OF "TEVILAS KELIM"
OPINIONS: The Gemara teaches that when a Jew purchases food utensils from a Nochri, not only must he perform the necessary procedures to remove the non-kosher food particles absorbed in the utensils, he must also immerse the utensils in a Mikvah. Even if he purchases a new utensil, he must immerse the utensil before he uses it.
The Gemara derives this requirement from two phrases in the verse. The verse says "v'Taher" and it says "b'Mei Nidah" (Bamidbar 31:23). Why are both phrases necessary? The Gemara explains that the term "v'Taher" implies that the utensils may be immersed in any amount of water. "Mei Nidah" teaches that they must be immersed in a Mikvah containing at least forty Se'ah of water. Had If the verse said only "Mei Nidah," it would have implied that a person must wait until sundown to use the utensil, and thus "v'Taher" teaches that it may be used immediately after Tevilah.
Is the obligation of Tevilas Kelim mid'Oraisa or mid'Rabanan?
(a) The fact that the Gemara finds it necessary to explain the two phrases in the verse implies that the verse is not merely an Asmachta for a Din d'Rabanan, but it is an actual source for a Din d'Oraisa. If the verse would be only an Asmachta for a Din d'Rabanan, then the Gemara would not be bothered with the necessity of each phrase, since there is nothing unusual in having two verses on which to base the Asmachta. This indeed seems to be the view of RASHI (DH Zuza), TOSFOS (DH Mayim), and the other Rishonim here.
(b) The RAMBAM (Hilchos Ma'achalos Asuros 17:5) writes that the immersion of utensils purchased from Nochrim is "mi'Divrei Sofrim." He adds that the "Chachamim said" ("Amru Chachamim") to add this extra act of Taharah. The wording of the Rambam clearly implies that he maintains that the obligation of Tevilas Kelim is only mid'Rabanan.
In truth, however, these words -- "mi'Divrei Sofrim" and "Amru Chachamim" -- alone do not prove that the Rambam considers Tevilas Kelim to be mid'Rabanan, because it is the style of the Rambam to refer to any law derived from the thirteen Midos sheha'Torah Nidreshes ba'Hen (the thirteen exegetical principles of expounding Torah law) as "Divrei Sofrim" (see Rambam Hilchos Ishus 1:2, and MAGID MISHNEH there). However, many Rishonim write that the Rambam indeed considers Tevilas Kelim to be mid'Rabanan. (See RITVA and RAN here, MAGID MISHNEH in Hilchos Yom Tov 4:18. Although the KESEF MISHNEH cites the RASHBA who writes that the Rambam maintains that Tevilas Kelim is mid'Oraisa, it is evident from the words of the Rashba that this is a typographical error and it should read instead "Ramban" in place of "Rambam.") Moreover, the Rambam earlier (17:3) uses the words "Divrei Sofrim" to refer to an Isur that is clearly mid'Rabanan.
The Ran adds that the Rambam is consistent with his own opinion elsewhere (in 17:6), where he writes that a person who is in possession of a utensil that he received from a Nochri as a Mashkon (collateral for a debt) does not need to immerse it in a Mikvah. In the Gemara here, this question is left unresolved, and the Rambam apparently is ruling leniently in accordance with his view that Tevilas Kelim is only mid'Rabanan, and thus the principle of "Safek d'Rabanan l'Kula" applies.
However, the HAGAHOS MAIMONIYOS (#8) cites Rishonim who write that even if Tevilas Kelim is mid'Oraisa, one may be lenient in the case of a Safek, since b'Di'eved one may use the utensil even without Tevilah, and, even l'Chatchilah -- since he has the option to use another pot (that does not need Tevilah) if he wants -- we allow him to use this pot without Tevilah. Therefore, we may be lenient in cases of doubt and not require Tevilah at all.
The RITVA writes that the Rambam's source is the fact that the Gemara derives the requirement to immerse Kelim in forty Se'ah from the verse that teaches that utensils acquired from Nochrim must be immersed. If the Gemara maintains that Tevilas Kelim is mid'Oraisa, then we would not be required to use forty Se'ah, because we never find that it is necessary to immerse a utensil that is Tamei in forty Se'ah in order to make it Tahor. Rather, it is sufficient for the water to cover the utensil on all sides, and even when there is less than forty Se'ah of water the Tevilah is valid to make the utensil Tahor. The Halachah that a utensil must be immersed in forty Se'ah is mid'Rabanan (Nazir 38a). Since the Gemara mentions forty Se'ah, it is evident that Tevilas Kelim is mid'Rabanan, and it is the Rabanan who required the Tevilah to be done in a Mikvah of forty Se'ah.
However, the Ritva cites the RAMBAN who refutes this proof. He says that when the Gemara mentions forty Se'ah, it means that mid'Oraisa there is an obligation to immerse the utensil in enough water to cover it, and mid'Rabanan one must immerse it in forty Se'ah. It does not mean that the Torah requires forty Se'ah, and it does not mean that the entire obligation of Tevilas Kelim is only mid'Rabanan.
TOSFOS (DH Mayim) suggests another answer to this proof. The verse regarding the utensils acquired in the war with Midyan gives a special requirement of Tevilah in forty Se'ah, even though Kelim (to become Tahor from Tum'ah) normally do not require forty Se'ah.
Are there any practical differences between whether Tevilas Kelim is mid'Oraisa or mid'Rabanan?
1. One practical difference is in a case of a Safek, such as in the case of the Safek in the Gemara (a utensil received as a Mashkon, collateral, from a Nochri), or a case in which a person is in doubt whether the utensil was immersed or not. As mentioned above, if the obligation of Tevilas Kelim is mid'Oraisa, then one would have to be Machmir in cases of doubt. If it is mid'Rabanan, then one may be lenient (except according to the Hagahos Maimoniyos, who maintains that even if Tevilas Kelim is mid'Oraisa, one would not have to be Machmir).
2. RAV MOSHE STERNBUCH shlit'a (in TESHUVOS V'HANHAGOS 1:449) suggests another practical difference between whether the obligation of Tevilas Kelim is mid'Oraisa or mid'Rabanan. Must one immerse an aluminum utensil that he buys from a Nochri? Aluminum is a metal that was discovered relatively recently; it was unknown at the time the Torah was given and during the times of the Gemara. The requirement of Tevilah for metal utensils is based on the verse that discusses the utensils the Jews received in the war against Midyan (Bamidbar 31:22). That verse mentions six different types of metals (gold, silver, copper, iron, tin, and lead). The fact that the verse mentions six specific names of metals and does not use a general term for all of them implies that only these metals require Tevilas Kelim, and one cannot derive through a Binyan Av that other metals require Tevilah. Rashi in Rosh Hashanah (19b, DH va'Chachamim) writes that the only "Klei Matachos" that can become Tamei mid'Oraisa are the six metals listed in the verse, and no others can become Tamei mid'Oraisa.
Rav Sternbuch suggests as follows. If the obligation of Tevilas Kelim is mid'Oraisa, then aluminum would not require Tevilah mid'Oraisa, because one cannot learn from the verse that any other material requires Tevilah. Would aluminum require Tevilah mid'Rabanan? The only item which the Rabanan added to the Torah's list is glass, and therefore there is no grounds for obligating aluminum in Tevilas Kelim, even mid'Rabanan. On the other hand, if the obligation of Tevilas Kelim is mid'Rabanan, then it is logical that when the Rabanan enacted this obligation they used the wording of the Gemara and instituted that "Klei Matachos" require Tevilah. Since they used the general term, aluminum should also be included in the obligation.
However, it can be argued that the law for aluminum does not necessarily depend on whether Tevilas Kelim is mid'Oraisa or mid'Rabanan. Even if Tevilas Kelim is mid'Oraisa, perhaps the six metals mentioned in the verse were meant to exclude any other materials which existed at that time (such as glass, which one might have thought should be included in the same category, since it can be molten; see Rashash to Rashi in Rosh Hashanah 19b). The verse does not intend to exclude materials that might be discovered in the future and that have similar characteristics to the six metals. Conversely, even if Tevilas Kelim is mid'Rabanan, the Rabanan may have instituted Tevilah only for those materials mentioned in the verse, since those are the ones that can become Tamei mid'Oraisa, as Rashi in Rosh Hashanah mentions. Although the Gemara uses the term "Klei Matachos," that is merely a shorthand reference to the types of materials mentioned in the Torah. Therefore, the Halachah regarding aluminum remains unclear. (See Insights to Chulin 25:3.)
HALACHAH: The SEFER TEVILAS KELIM (by Rav Tzvi Cohen, 11:142, footnote 113) cites the TIFERES YISRAEL in his introduction to Taharos (#44) who says that newly discovered metals have the same status as the old metals. Therefore, he rules that, in practice, aluminum utensils must be immersed in a Mikvah with the appropriate blessing.
2) THE UTENSILS OF A CONVERT
OPINIONS: The Gemara teaches that utensils purchased from a Nochri require Tevilah. What is the Halachah regarding the utensils of a Nochri who converts and becomes Jewish? Must he immerse all of his utensils, just as a Jew must immerse the utensils that he acquires from a Nochri?
(a) This question may depend on the logic behind the obligation of Tevilas Kelim. If the guidelines of the obligation of Tevilas Kelim are similar to the guidelines of the prohibition of Stam Yayin -- which the Rabanan instituted in order to distance Jews from Nochrim ("Harchakah"), then a Ger would not need to immerse his Kelim, because he does not need to distance himself from his previous self! However, the Rishonim cite the Yerushalmi (Avodah Zarah 5:15) which states that the obligation of Tevilas Kelim is not for the purpose of "Harchakah," but it is because the Kelim are leaving the Tum'ah of Nochri-ownership and entering the Kedushah of Jewish-ownership. The Tevilah is similar to the Tevilah of a person who is Tamei, who immerses in order to elevate himself to Kedushah. Therefore, a Ger's utensils should require Tevilah in order to elevate them from Tum'ah to Kedushah, just as the Ger himself requires Tevilah to elevate himself to the Kedushah of Yisrael.
In fact, the RAMBAN (cited by the Ritva here) writes that the verse compares the Tevilah of Kelim to the Tevilah of a Ger, and that is why it must be done in forty Se'ah (rather than in just enough water to cover the utensil). RAV MOSHE STERNBUCH shlit'a (in TESHUVOS V'HANHAGOS 1:451) cites the RASHBA in Yevamos (47b) who makes a similar comparison between the Tevilah of a Ger, which is done only after Milah, and the Tevilah of Kelim, which is done only after the non- kosher food particles absorbed in the Kelim have been removed. Accordingly, the Kelim of a Ger should require Tevilah, just as the Ger himself needs Tevilah.
According to the reasoning of the Yerushalmi, why do only metal Kelim require Tevilah, and why is it that only Kelim used for food require Tevilah? Any item acquired from a Nochri should require Tevilah, since it needs to attain the Kedushah of Jewish-ownership! The RITVA here (DH Klei Se'udah) answers that metal Kelim, even if they are new and have not yet been used, are considered more Tamei than other Kelim since they are destined to be used for forbidden food items and to absorb non-kosher food. Therefore, when they are purchased by a Jew and will now be used only for permitted food, they are being elevated from Tum'ah to Kedushah.
(b) The SEFER TEVILAS KELIM (p. 245) cites the words of RAV YITZCHAK DOV BAMBERGER as quoted in the periodical, ha'Ma'ayan (5739). Rav Bamberger cites proof to exempt the utensils of a Ger from Tevilah after he converts. Hash-m taught Moshe Rabeinu the Mitzvah of Tevilah for Kelim made by a Nochri only after forty years in the Midbar, at the time of the war with Midyan. Why did He wait until then to teach this law? Did they not need to know it earlier? The obvious answer is that they did not acquire any utensils from Nochrim until that point, when they conquered Midyan and took their Kelim, and thus they did not need to be taught that Mitzvah earlier. However, from the verses it seems that the Jews did acquire gold and silver Kelim from Nochrim earlier. At the time of Yetzi'as Mitzrayim, they took the Kelim of the Mitzrim (Shemos 12:35)! Those Kelim probably included eating utensils as well. Why, then, were they not taught the Mitzvah of Tevilas Kelim at that time? The obvious answer is that they were not yet given the Torah, and just as other Halachos did not apply to them at Yetzi'as Mitzrayim, this Mitzvah was not yet given to them.
However, the question remains, why were they not taught the Mitzvah of Tevilas Kelim at the time of the giving of the Torah at Har Sinai, when they still had the Kelim of the Nochrim in their possession? (It is understandable that they did not need to be taught the Mitzvah of Hag'alah, because the Kelim were not "Bnei Yoman," and thus mid'Oraisa they did not require Hag'alah, as the Gemara says on 76a. In addition, since the Jews already cooked in the Kelim, the cooking removed the Beli'ah of Isur which the Kelim had absorbed, in a permissible manner before the Beli'ah became prohibited.)
Rav Bamberger writes that apparently Tevilas Kelim was not necessary, because the Kelim already were in the Jews' own hands before the giving of the Torah, and they did not receive them from Nochrim after the giving of the Torah. Accordingly, it may be inferred from the fact that the Jews were not commanded to immerse their utensils when they became Gerim at Har Sinai that there is no requirement for a Ger to immerse his own utensils when he converts! The reason for this is that the Torah requires Tevilah only for utensils similar to Klei Midyan, which the Jews obtained through an actual transfer of possession.
What is the logic behind this distinction? If the Torah requires Tevilah only for utensils similar to the Klei Midyan, then Tevilah should be required only for utensils obtained in times of conquest and not for utensils obtained from Nochrim through a gift or through purchase.
Perhaps the logic to differentiate between Kelim purchased from a Nochri and Kelim of a Ger is that a Ger is required to immerse himself in order to raise his own Kedushah to that of a Yisrael. Once he raises his own Kedushah, the Kedushah of all the items that are subordinate ("Tafel") to him -- such as his utensils -- is raised along with him. Consequently, he is not required to immerse his Kelim separately.
If this approach is correct, then it may provide a way to refute the proof of Rav Bamberger. Perhaps the only time at which the utensils of a Ger were elevated along with the Ger is when the nation became Jewish at Har Sinai, when they became Jewish as an entire nation and not merely as individuals. The reason for this difference is that before the conversion of the Jewish people, there did not exist a Kedushah of Yisrael, and their Gerus created such a Kedushah. Just as it created a Kedushah for themselves, it created that Kedushah for their utensils. However, after that time, whenever a Ger converts the Kedushah of Yisrael already exists. The Ger merely attaches himself to that existing Kedushah. Perhaps his Gerus serves to attach only himself to the Kedushah of Yisrael, but not his utensils, and therefore his utensils require a separate Tevilah.