Tosafos there also quotes a medrash that says that the reason that we read the parshah of the arayos is to remind Hashem that just as we are commanded not to commit any aveirah with arayos, so too Hashem should not be megaleh ervasom beavonesem (commit an act of arayos with Bnei Yisrael’s sins).
The sefer Harirai Kedem suggests that these two different reasons regarding the reading of the parshah of arayos could be dependent on the machlokes mentioned above. According to the Mechaber the reading of the Torah at Minchah on Yom Kippur results from the kedushas hayom; therefore we read a portion that relates to the kedushas hayom (namely, as the medrash explained, that Hashem should not punish us for our sins). According to the Rema’s view that we read the Torah at that time, as we would on any fast day when the essence of the Torah reading is primarily to rebuke the congregation, the portion that we read should be of rebuke (namely, as Rashi and Tosafos explained, to remind people not to do aveiros – and to do teshuvah).
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