Genèse 32:33

Therefore the sons of Israel eat not the sinew which shrank, which is in the hollow of the thigh of cattle and of wild animals, until this day; because the Angel touched and laid hold of the hollow of the right thigh of Jakob, in the place of the sinew which shrank.

על כן לא יאכלו, as a reminder of the heroism displayed by Yaakov, as well as a reminder of the miracle that G’d performed for him as a result of which he did not die.

על כן לא יאכלו בני ישראל, in order to ensure that the damage inflicted to Yaakov’s offspring as predicted by the angel should be kept to a minimum as long as they remind themselves of the symbolic meaning of that injury suffered by Yaakov during his nocturnal encounter with this angel. [I believe that even commentators who concentrate on the plain meaning of the text, such the ones whose commentaries I am translating in these volumes, feel free to treat the text allegorically when the narrative of the Torah itself appears pointless unless we understand it in historical terms, offering moral and ethical teachings and warnings of long term significance. Ed.] Alternatively, the moral lesson is that just as the gid hanashe is totally devoid of taste, does not appeal to the palate, so that consuming it would not provide the sinner with any kind of gratification, we are taught not to second-guess G’d’s legislation by treating this commandment as not important.

על כן לא יאכלו בני ישראל, the children of Yaakov adopted this prohibition for themselves in commemoration of their father whose thigh muscle had been injured. They in turn commanded their children to abstain from eating this part of any animal. This continued until the Torah was given and it became law. It reminds us of the descendants of Yonadav ben Rechev who faithfully adhered to the clan’s founding father’s injunction not to drink wine (Jeremiah 35,6) in honour of the oath they swore to their forefather. They are described as loyalists par excellence in the Book of Chronicles. Moses recorded the custom of the Israelites not to eat this organ as one of the 613 commandments. Although the Torah does not generally consider it necessary to justify G’d’s legislation with a reason, in this case, since this law had been observed as a Jewish tribal custom for so many hundreds of years prior to the giving of the Torah, we are told how the custom which became enshrined in Torah law originated.

את גיד הנשה, our sages in Chulin 91 explain the name of this muscle or ligament (sciatic nerve) as due to the fact that it is apt to move from its original location, from the spoon shaped joint to which it is attached.

אשר על כף הירך, the only part of the sinew prohibited by Biblical injunction is the part directly attached to the hip joint.. What is above and below is forbidden by Rabbinic decree. Similarly, the exterior sinew is also only forbidden by Rabbinic decree (Chulin 91) The prohibition applies equally to domesticated beasts, free roaming beasts, as well as to the שליל, the as yet unborn embryo. The prohibition applies to both the right and the left hind leg of the animal, even though the sages are agreed that only one of Yaakov’s sciatic nerves was injured as seems clear from the words (singular) “he dislocated the sinew of the thigh-vein.” The halachic ruling follows the view of Rabbi Yossi that although only one sinew was injured they are both forbidden to be eaten. The fatty tissue on top of these sinews is also forbidden as a Rabbinic injunction.

על כן לא יאכלו בני ישראל, “therefore the Children of Israel to this day do not eat the thigh muscle, etc.” the words על כן here mean: ”as a permanent reminder of” the miracle that had saved their founding father in his contest with the angel who had only been able to inflict a minor injury on him, instead of killing him as he had intended. The undertaking is similar to a person who after suffering for long periods from headaches or and pains in the region of his heart, vows not to eat the head or the heart of an animal forthwith, as a sign of gratitude for having been healed. An alternate interpretation. The words על כן, mean: “as a result of this,” i.e. as a result of having narrowly escaped death as a result of having remained exposed to danger alone during the night, the Israelites learned that this is not the correct way to behave at night and alone. Abstaining from eating the thigh muscle is the visible reminder of the fact that this lesson had been internalised by the people as an inadmissible way to behave. Yaakov’s wives and children accepted part of the responsibility for their leader’s injury by having allowed him to cross the river alone at night and thus having exposed him to danger. This is why G–d forbade them (his descendants the Jewish people) to eat this part of the animal. They should be meticulous in observing the commandment to give people safe conduct. This is why already Yaakov was commanded to give Joseph safe conduct on his fateful mission. (Genesis 37,14) [where he accompanied him part of the way where he might be exposed to danger by the Canaanites. Ed.]