Musar zu Bereschit 41:28

(Ibid. 14): "And he [Jacob] sent him [Joseph] from Emek Chevron" — "from the deep [(alluded to by "Emek")] counsel of that tzaddik [Abraham] buried in Chevron, in fulfillment of what was stated (Ibid. 15:13): 'for your seed will be a stranger in a land that is not theirs.'" The meaning here (in my humble opinion) is that Egypt was the "nakedness of the land," an extremely impure place, for which reason it was ordained in the beginning that one of the sons of Jacob would come to publicize there [in Egypt] belief in the Divine providence, as it is written (Ibid. 41:25): "What G-d is to do He has shown to Pharaoh." For a similar reason Joseph commanded afterwards that they [the Egyptians] circumcise themselves — all to weaken the power of impurity, so that it would be fit afterwards for Israel to sojourn there.