Thought for the Day: Immersing a New Pot On Shabbos

The Shulchan Aruch (323:7) brings a machlokes whether or not it is permitted to immerse a new pot (that was bought from a non-Jew and thus requires immersion before using it to cook food) on Shabbos.  We typically don't worry about tuma nowadays, so when we think of immersing keilim, we are usually thinking about pots, pans, hot water urns, and the like that we recently acquired or received as a gift.  In order to understand this machlokes, however, we need to be more broad minded.  There are two basic factors that contribute to this machlokes.  First, while pots and pans are keilim, so are blankets and sofas.  Second, there are two reasons one might want to tovel a keili: (1) remove the tuma; (2) allow a cooking utensil that was acquired from a non-Jew to be used.   (More details about what a keili is and under what circumstances it need to be immersed can be found here: A Deep Dive Into T'vila.)

The biur halacha (d.h. mutar l'hatbil v'chulu v'yeish osrim v'chulu) explains the machlokes based on the four reasons given (TB Bei'a 18) that Chazal forbade immersing tamei keilim (vessels/clothing) even on Yom Tov:

1. Raba says it is a hedge (g'zeira atu) against carrying in a public domain on Shabbos (ie,  against not even within an eiruv because sometimes there isn't an eiruv; not even on Yom Tov because folks sometimes mix up what is allowed on Shabbos with what is allowed Yom Tov).
2. Rav Yosef says it is a hedge against wringing out clothes after immersion (not even non-absorbent keilim because of absorbent keilim).
3. Rav Bibi says it to prevent people from keeping tamei pots around their house till they have all that free time on Yom Tov and Shabbos, and in the meantime forgetting themselves and cooking up some yummy t'rumah in a tamei pot.  T'ruma cooked in a tamei pot needs to be destroyed; a serious offence.  (So all Jews because of cohanim.)
4. Rava says because is similar to repairing a vessel.

The Ri"f brings only the reasons given by Rav Yosef and Rav Bibi.  Note that neither of those reasons apply to pots and pans that need to be immersed before first use.  Rav Yosef's reason doesn't apply, because pots and pans are not absorbent and never need to be wrung out.  Rav Bibi's reason doesn't apply because cooking food in an untoveled pot does not assur the food.  It is certainly forbidden to use that pot (perhaps even d'oraisa), but the food is not damaged in any way.  (Good to know if you are offered coffee cooked by a non-frum Jew using their untovled coffee maker.)  Therefore, the Ri"f paskens it is permissible to immerse pots and pans for first use, even on Shabbos.

Ro"sh paskens that the issur is due to the reasons brought by Raba and Rava.  Both those reasons -- a hedge against carrying in the public domain and because it looks like fixing -- have nothing to do with the use of the keili or why it needs to be immersed.  Hence, the Ro"sh paskens that it is forbidden to immerse pots and pans for first use, even on Yom Tov.

This seems to be one of those cool cases where you can see reflected in halacha l'ma'aseh how the rishonim learned a gemara.  The Ri"f is learning that the four reasons given apply to specifically to the immersion of keilim to m'ta'her them; therefore he only brings the reasons of Rav Yosef and Rav Bibi when it comes to the immersion of new keilim for cooking.  The Ro"sh, on the other hand, is learning that (to paraphrase a not-so-recent-ad-anymore) "keilim are keilim"; the g'zerios immersion to m'ta'her apply equally well to immersion of new cooking vessels.