Musar su Genesi 32:33

The following is the way the Zohar and other Kabbalistic books explain the mystical dimension of the prohibition of this commandment. Man's various limbs are perceived as branches of the מרכבה in the higher regions The Torah has given us 248 positive commandments which correspond to each one of the 248 limbs of אדם העליון man's counterpart in the spiritual regions. Kabbalists speak of 248 angels bearing the name of their Master. These angels are perceived as the clothing of the שכינה. There are also 365 branches of דין, Justice, on the "tree" in the "upper regions," corresponding to the 365 days of the year and the 365 sinews of man. There is both a sinew and a negative commandment for every day of the year, and the ninth of Av is the day which corresponds to the prohibition of the גיד הנשה. Our sages saw an allusion in the extra word את in על כן לא יאכלו בני ישראל את גיד הנשה (Genesis 32, 33), to include תשעה באב [a day when any food intake is prohibited anyways]. They also included סמאל ויצה"ר Satan and the evil urge. Both the eating of that sinew and profiting from it in some other manner is prohibited. Neither Israel, nor any of its limbs could be defeated on any other calendar date, nor could any other sinew have succumbed to its adversary except the גיד הנשה. Only on that date was the power of דין strong enough to undermine the strength of Israel. On that date G–d abandoned us in exile, until a wind (spirit) will blow from the Heavens. Anyone who eats on the Ninth of Av, is considered as if he had eaten the גיד הנשה.

“Therefore the Children of Israel do not eat the sciatic tendon” (Genesis 32:33). The sciatic tendon is forbidden in benefit, so it is forbidden to give it to one’s Canaanite slave or maidservant. And it is forbidden to send a thigh (as a gift) to a Canaanite with the sciatic tendon inside it. (And likewise does Rosh bring in the name of [Rabbeinu Yonah] at the beginning of the chapter [entitled] Gid HaNashei in the discussion of a man sending a thigh to a Canaanite. But we do not establish [the law to be] like him in this, but rather like the opinion of Rambam - that the sciatic tendon is permissible in benefit, so one may send a thigh to a Canaanite with the sciatic tendon inside it. And it is explained in Tur and Shulchan Arukh, Yoreh Deah 65.)