The Torah in Parashat Tetzaveh describes the me’il, the special robe worn by the kohen gadol, which was to have a special “safa” (binding) around the neck (28:32). This verse concludes, “lo yikarei’a” – “it shall not tear,” seemingly explaining the purpose for the “safa” – to ensure that the material around the neck does not tear.
The Gemara, however, in Masekhet Yoma (72a), comments that the words “lo yikarei’a” establish a Torah prohibition against ripping the me’il – a prohibition which is then extended to include all the priestly garments. Although this phrase appears to simply explain the reason behind the requirement to add extra material around the neck, the Gemara insists that it in fact introduces a Biblical command. The Gemara explains that if “lo yikarei’a” merely gave the reason for the “safa,” then it would have been written, “she-lo yikarei’a” – “so that it would not tear.” The fact that the Torah says simply, “lo yikarei’a” indicates that this phrase should be taken as a separate command not to tear the garment.
Rabbi Akiva Eiger, in Gilyon Ha-Shas, raises the question of how to reconcile the Gemara’s comment with the Gemara’s discussion in Masekhet Sanhedrin (21a) regarding the command in Sefer Devarim (17:17), “And he [he king] shall not have many wives,” a verse which concludes, “ve-lo yasur levavo” – literally, “and his heart shall not turn away.” The Gemara there explains the second segment of this verse as providing the reason for the first: a king is prohibited from marrying too many women, as this could result in his heart being turned away. This interpretation, seemingly, runs in direct contradiction to the Gemara’s discussion in Masekhet Yoma regarding the me’il. If “lo yikarei’a” must be read as a command because it is not written as “she-lo yikarei’a,” then by the same token, the phrase “ve-lo yasur levavo” should be read as a separate command, since the Torah does not say, “she-lo yasur levavo” (“so that his heart is not swayed.”
Rav Yerucham Perlow, in his commentary to Rav Saadia Gaon’s listing of the Torah’s commands (vol. 2, mitzva 214), writes that these Talmudic passages suggest that this issue is a matter of debate among the Sages. Apparently, the Gemara in Masekhet Sanhedrin did not accept the Gemara’s premise in Masekhet Yoma that the prefix “she-” (“so that”) is necessary for a phrase to be understood as an explanation for the preceding phrase. Accordingly, the Gemara in Masekhet Sanhedrin does not accept the position that “lo yikarei’a” constitutes a prohibition, and instead interprets this phrase as simply an explanation for the requirement to add a “safa” along the neckline of the kohen gadol’s robe.
On this basis, Rav Perlow explains why Rav Saadia Gaon did not include in his listing of the mitzvot the prohibition of “lo yikarei’a.” Rav Saadia evidently sided with the view expressed in Masekhet Sanhedrin, and thus did not understand this phrase as a command. Similarly, Rav Saadia does not include in his list the prohibition established by the Gemara there in Masekhet Yoma against separating the kohen gadol’s breastplate from his apron. The Torah (28:28) requires fastening the breastplate to the apron with threads and hooks, adding, “ve-lo yizach ha-choshen mei-al ha-eifod” – “and the breastplate shall not come loose from the apron.” Here, too, this phrase appears to explain that the breastplate should be tightly fastened to the efod in a manner that does not allow it to become loose, but the Gemara in Yoma interprets this phrase as a prohibition against separating the two garments from one another. Rav Saadia Gaon, apparently, felt that the view expressed in Masekhet Sanhedrin is the accepted position, and thus he did not accept the interpretation of “ve-lo yizach ha-choshen” as a Biblical command, just as he did not accept the interpretation of “lo yikarei’a” as a Biblical command. (Rav Perlow applies this theory also to explain why Rav Saadia Gaon did not include in his list the Torah’s comment regarding the poles affixed to the sides of the aron – “lo yasuru mimenu” (25:15), which the Gemara in Yoma understands as a prohibition against removing the poles that were affixed to the ark.)