The Torah in Parashat Beshalach tells about the manna which fell miraculously each morning to feed Benei Yisrael during their sojourn in the wilderness.  We read that on Friday morning, God provided each member of the nation with a double portion, as no manna fell on Shabbat morning: “On the sixth day, they collected a double portion of bread, two omer’s for each person” (16:22). 

            The Gemara in Masekhet Shabbat (117b) cites this verse as the source for the requirement of lechem mishneh, the use of two loaves of bread at the Shabbat meal.  The Arukh Ha-shulchan (O.C. 274:1) explains the Gemara’s inference as based upon the seeming superfluity in the Torah’s account of the double portion.  As the Torah had already informed us that on other days each person received one omer (16:16), there was no reason for the Torah to mention that on Friday they collected “a double portion of bread” and “two omer’s for each person.”  It would have sufficed to simply say that they collected two omer’s, without emphasizing that they received “a double portion of bread.”  The Gemara therefore concluded that the Torah added the phrase “lechem mishneh” to establish the protocol for Shabbat meals for future generations. 

            The Arukh Ha-shulchan further comments that in his view, the Gemara refers here to an outright Biblical source, and thus lechem mishneh constitutes a Torah obligation.  This is in contrast to other authorities, who maintained that using two loaves on Shabbat is required by force of rabbinic enactment.  For example, the Magen Avraham (188:9) cites the Ran and Talmidei Rabbenu Yona as asserting that there is no Torah obligation to eat bread at all on Shabbat, in which case the requirement of lechem mishneh must certainly have been introduced by Chazal.  The inference from the verse here in Parashat Beshalach, according to this view, is an “asmakhta,” a subtle allusion in the text to a law ordained later by the Sages.  The Sedei Chemed (vol. 4, p. 51) similarly cites Rav Shlomo Kluger and Rav Yosef Shaul Nathanson as commenting that lechem mishneh constitutes a rabbinic, rather than Biblical, obligation. 

            The Arukh Ha-shulchan, however, as mentioned, disputes this position, and claims that two loaves are required on the level of Torah obligation.  This is also the view of the Taz, who, in the context of the laws of Chanukah (O.C. 678:2), writes that a person with limited funds should give priority to lechem mishneh over Chanukah candles, as the former is required by Torah law. 

            Rav Aharon Yehuda Grossman, in his Ve-darashta Ve-chakarta, draws proof to this view from the Gemara’s account of Rav Kahana’s practice to hold two loaves while reciting the berakha but cut only one loaf (which is, indeed, the prevalent custom).  In defending his practice to slice and partake of only one of the two loaves, Rav Kahana noted the verse from which the obligation of lechem mishneh is inferred: “laketu lechem mishneh” – “they collected a double portion.”  The Torah in this verse speaks only of the people’s collection of a double portion, but does not record their consumption of a double portion.  And since this verse establishes the requirement of lechem mishneh, this obligation refers only to holding two loaves of bread, but not necessarily eating from two loaves. 

            If Rav Kahana reaches conclusions regarding the halakhic details of lechem mishneh based upom this inference, it stands to reason that he viewed it as a bona fide Biblical source, thus suggesting that lechem mishneh is indeed a Torah obligation.