A Son of Grace
This is the last parsha in the book of Bereishis. In it Jacob bids farewell to his twelve sons before his death. He gives them, individually, his blessings. We will look at his blessing to his favorite son, Joseph.
"A son of grace is Joseph; a son of grace to the eye; girls mounted the wall (to see him)."
Ben Porat - RASHI: [This] means a son of grace (Hebrew "hain") (Rashi then cites an Aramaic phrase that shows that "porat" means grace).
Ben Porat to the eye - Rashi: His grace is directed towards the eye that sees him.
Girls mounted the wall - Rashi: The girls of Egypt mounted the wall to gaze at his beauty.
WHAT IS RASHI SAYING?
Rashi's interpretation differs from the Targum Onkelos's. Onkelos understands the word "porat" to mean "fruitful." Rashi prefers "graceful."
Can you see why Rashi chose "grace" over "fruitful"?
An Answer: Joseph had only two sons. This is not particularly "fruitful" compared to his brother Benjamin who had ten sons. Also, Joseph was known to be a person with charm or grace ("hain"). See 39:4 and 39:21. So Rashi's interpretation would seem more in line with what we know about Joseph.
But we can question Jacob himself (not Rashi, this time). Even if Joseph was a charmer, is this the one trait that Jacob must pick to bless his son? Joseph had so many other talents – dream interpreter, prophetic dreamer, brilliant CEO of the world's most advanced country (Egypt) in a time of national disaster. Why would Jacob choose Joseph's beauty to emphasize?
An Answer: I would say that Jacob stressed it because the Torah had stressed his beauty up until now. See Rashi on 37:2 and see verses 39:4 and 39:21 and of course Pharaoh's love of Joseph. Granted this was due to Joseph's ability to interpret dreams, but Joseph must have related to Pharaoh in a way that found favor in his eyes. (His modesty among other traits and modesty is a major part of "hain."). Therefore, I think, Jacob stresses this aspect of Joseph. His beauty was his strength, when it could have been his downfall (had he given in to Potifar's wife's enchantments). It was his strength when God had him find favor in the eyes of those people who could propel Joseph forward. Joseph used this beauty - "hain" - in a modest way (see all his statements of disclaiming credit for his successes). So his beauty was the underlying aspect of his success and nevertheless Joseph does not take advantage of it nor does it go to his head.
So Jacob chose a central aspect of Joseph's personality which he wisely controlled and used exclusively in the service of Hashem.