This weeks parsha, Vayechi.
In the blessing for Yosef, in one way in Rashi, Yaakov blessed him because he extended his height so that Eisav should not look on his mother. The question is, what was Yosef scared of? If Rochel thought before that due to her being barren Yaakov will divorce her and Eisov may marry her, but now when she had Yosef and was expecting Binjomin what was she worried for?
The answer is that it is bad for a person to be the reason for someone else’s stumble even if they did not participate. For Eisav it is a sin to gaze at Rochel regardless how much evil he has done already and Rochel will be the cause to it, so Yosef shielded her from Eisav eyes in order to protect her.
This is one of the big explanations of modesty, as the gemoro tells a story of an amoire who saw his neighbor digging a hole in the wall separating their gardens, on his question the neighbor answered “ if I can’t marry your beautiful daughter let me at least look at her through the wall” Upon hearing this the amoira turned to his daughter and said “ people are sinning because of you? Go back to your earth!” and she died.
The question is what reward was it for Yosef that the girls in Egypt climbed on the walls to see his beauty?
The answer could be as we see in the gemoro that R’ Yochanan sat himself on the path used by the woman returning from Mikva, and he explained that when they look at him the will get children like him. From that Gemoro we see that looking at a tsadik brings upon a person the merit of having children like the tsadik and one is allowed to do this.
Just like we said above that it’s bad for a person to be the cause of an aveire, the same thing it is good for person to be the reason for a mitsve done, so this was Yosef’s reward, Mida Keneged Midah, that the Egyptian woman who looked at him had better children.
Maybe this explains the existence of g-d fearing Egyptians who kept their cattle in doors when Moshe warned them about the plague “dever”.