"And he resided there" - [This] teaches that Yaakov, our father, didn't go down to settle in Egypt, but rather [only] to reside there, [temporarily],as it is stated (Genesis 47:4), "And they said to Pharaoh, 'To reside in the land have we come, since there is not enough pasture for your servant's flocks, since the famine is heavy in the land of Canaan; and now please grant that your servants should dwell in the Land of Goshen.'"
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On a conceptual level, why did Bnei Yisrael descend to Mitzrayim specifically when they reached the number 70?