Why We Recite Shema Before a Bris

At a vacht nacht (a seudah held the night before a bris milah to protect the baby boy, during which divrei Torah and keriyas Shema are recited), the Imrei Chaim of Vizhnitz told over the following. After all those present had recited keriyas Shema, as is customary, he related that Rav Pinchos of Koretz once asked Rav Mordechai, the chazzan of Zaslov, "You perform at many simchas and recite Shema at many vacht nachts. Tell me, why do we recite keriyas Shema on the night before the bris?" The chazzan answered, "Chazal ask (Berachos 13a) why the parsha of Shema precedes the parsha of V'haya im shmoa. They answer that first we accept upon ourselves the yoke of the Kingship of Heaven, and only afterwards the yoke of the mitzvos. Based on this, the custom is easily explained. Since this baby will enter the yoke of the covenant of mitzvos tomorrow, we must first accept the yoke of Hashem's Kingship, so we recite Shema on the night before the bris."