What does Genesis 47:29 mean?
It's not clear exactly when this conversation took place. Jacob came into Egypt speaking as if he was about to die (Genesis 46:30), only to live another seventeen years (Genesis 47:28). Whenever it happened, it's in a moment when Jacob is planning for the aftermath of his own death. He has successfully resettled his large family in Egypt, and they are thriving (Genesis 47:27). He knows the family will not be leaving this area any time soon. A key concern in Jacob's mind is burial: he doesn't want his remains to stay in Egypt. He wants to be interred with his ancestors, in Canaan (Genesis 47:30).Jacob calls Joseph to his side and puts his request to Joseph very formally. The expression "if I have found favor in your sight" implies an obligation on the person being asked, while also expressing humility. This is an extremely important issue for Jacob. It's critical enough for Jacob to request a common, solemn gesture of promise. This is a guarantee that Joseph will make this request happen.
As was Abraham's servant (Genesis 24:2–3), Joseph is asked to put his hand "under my thigh" and swear a promise. In practice, this likely meant putting the hand just below, or even on, the genitals. Symbolically, the promise is being associated with the descendants of that person. Joseph is not merely vowing to Jacob, but to all of Jacob's posterity. In some cultures, this gesture also implied that breaking the oath would be avenged by those descendants.
Strange as this seems to modern readers, the same intent is used in more recent practices. Legal witnesses or political appointees would often place their hand on a Bible to swear an oath. Symbolically, their promise is also being made to God; Joseph's vow is also being made to Jacob's future line.
