Post: Chizkuni addresses the above question, and offers a number of answers:
- It is a fine and punishment, for Yaakov's sons left him alone. They were, after all, strong men. They should have stayed to help him and, because they did not, Yaakov was injured.
- Since Yaakov was able to survive the attack and prevail against the angel, the not eating of the gid hanesheh is to make a remembrance of this glory.
- Because he was injured in that specific part of his body, his descendants accepted this upon themselves. This akin to someone who has a specific body part which aches, he might accept not to ever eat from that body part in order that his own body part should get better. (Thus, it seems, some spiritual national impact is being counteracted.)
The Sefer HaChinuch explains in a different manner:
Namely, that this does serve as a reminder, but that the nation of Israel will survive through galus, which will then act as an encouragement to keep within our faith and righteousness. After all, this was a struggle with the sar of Esav, representing the nations of the world. And though the angel did manage to pain Yaakov in the struggle, eventually, Yaakov prevailed, and the sun healed him. So too, the sun of Moshiach will shine for us and heal us from our suffering, and he will redeem us, Amen, speedily in our days.
I wonder whether this sort of zikaron works so well nowadays. After all, we are far removed from our meat production. Our meat doesn't come from cows -- it comes from the supermarket. Add to this that Ashkenazim typically avoid the entire bottom half of the cow, because of difficulties in removing the sciatic nerve. Thus, even earlier in the production line, nobody is specifically removing it. I wonder if the pasuk serves as an effective reminder as the actual removal of only that part, and the customer being aware that this has been done for his piece of meat...