출애굽기 1:7 해설: Rashi, Rashbam, Sforno & Chizkuni

That there women did not miscarry and did not die when they were young.

פרו, the number of pregnancies;

פרו וישרצו, after the last of the original 70 migrants had died, their whole lifestyle became more like that of creeping insects, creatures headed for destruction. This is why when ויקם מלך חדש על מצרים אשר לא ידע את יוסף, although there can be no question that in the annals of Egyptian history the 80 year reign of Joseph and his legislation saving Egypt from the famine was duly recorded, as well as how he legislated that the whole land would belong to Pharaoh and the farmers would become his tenants, it did not occur to anyone to associate the Hebrews of his time with the family of Joseph who had been so highly esteemed. The idea that the present day Hebrews deserved special consideration on account of their illustrious forbears did not occur to anyone observing the way these Hebrews behaved at that time.

וישרצו AND THEY INCREASED ABUNDANTLY (more lit., they swarmed, a word used of the prolificness of reptiles) — they bore six children at one birth (the six words from פרו to מאד suggest or imply the number six) (Midrash Tanchuma, Shemot 5).