21:22כ״א:כ״ב
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ויהי בעת ההיא - שנולד יצחק משרה וידע אבימלך נסים שעשה לו הקב"ה, לכך בא עתה לכרות ברית עמו. וכן כל בעת ההיא צריך לפרש לפי המאורע.

ויהי בעת ההיא, at the time when Yitzchok was born by Sarah and Avimelech had become a first-hand witness to the miracles G’d had performed for Avraham. This is why he and his chief general were now interested in concluding an alliance with Avraham. Every time the expression בעת ההיא occurs it must be understood in terms of happenings immediately preceding the ones to which the next paragraph is linked.