Musar sur Les Proverbes 4:5

We view the number 7 as corresponding to the 7 days that are called by the Kabbalists the seven days of בנין, the days of Creation. Jacob, whose attribute is represented by the emanation תפארת, embodies within himself all seven stages of that בנין. Joseph, who was the direct continuation of Jacob, i.e. תפארת, also embodied all seven stages of the בנין. This is why there were in Pharaoh's dream twice seven cows and twice seven ears of corn. Together that makes 14 cows, corresponding to the 14 tribes. The ones that rose "on one stalk," symbolise the בנין in the "upper" regions above the emanation of תפארת, the region made up of the emanations חכמה, בינה. Here we come to the mystical dimension of the word אז whenever it is used in the Torah. The letters ז are perceived figuratively as "entering” the main stem of the letter א. This is possible because that letter is rooted in the emanation בינה. That emanation forms part of the three highest emanations which are one unit (in certain respects). When Solomon advises in Proverbs 4, 5: קנה חכמה קנה בינה, "acquire wisdom, acquire discernment,” the repetition of the word קנה, alludes to its dual meaning, i.e. its meaning is also Kaneh, stem, shaft. There is a single shaft to which the emanations חכמה, בינה, דעת are attached, and we may view this as similar to the shape of the letter א. The number "seven” as represented by the letter ז, is attached to that main shaft of the א from either side, hence we have the number 14.

What all this has to do with Samael injuring the כף ירך יעקב, the thigh joint of Jacob, is simple. Our sages say on 32,26: וירא כי לא יוכל לו, ויגע בכף ירכו ותקע כך ירך יעקב, that the thigh joint of Jacob refers to the later descendants who experienced the harsh decrees by the various nations who were their hosts in exile. When the Hasmoneans overcame the Greeks, they reversed this injury, i.e. the כף became a פך a cruse of oil. What had been a vulnerable part of Jacob's ירך now became the solid basis of the candelabra, ירך מנורה.