Midrash su Genesi 48:17

R. Samuel the son of Nahman stated: The Holy Spirit forsook Jacob twice. Once when he wished to bless Manasseh and Ephraim, and again when he was about to reveal the time of redemption. And Israel stretched out his right hand, and laid it upon Ephraim’s head (Gen. 48:14). He began to bless him with the words: And let them increase like fish (ibid., v. 16). He thus indicated that Ephraim’s descendants would be caught like fishes, as it is said: Say now “Shibboleth”; and he said “Sibboleth” (Judg. 12:6).¹¹Just as fishes are caught by their mouths, so too forty-two hundred Ephraimites were killed because they could not pronounce the word Shibboleth correctly. When Joseph saw that his father was laying his right hand on the head of Ephraim, it displeased him and He held up his father’s hand, to remove it (Gen. 48:17). Jacob rebuked him, saying: “Do you seek to turn away the hand that vanquished the foremost among the angels?” R. Yohanan said: Jacob’s arms were like two columns in the public baths in Tiberias. And Joseph said unto his father: “Not so, my father, only this one is the firstborn” (ibid. , v. 18). And his father refused and said: “I know it, my son; I know it” (ibid., v. 19). He foresaw that Gideon would descend from Manasseh, but that his younger brother was the more important one, since Joshua would descend from him. And he blessed them that day, saying: “By thee shall Israel bless, saying: God make thee as Ephraim and Manasseh” (ibid., v. 20). He mentioned Ephraim before he mentioned Manasseh. When was his blessing finally fulfilled? At the time of the consecration of the chiefs. Then Ephraim brought his offering on the seventh day, and Manasseh on the eighth, in fulfillment of the scriptural verse: That confirmeth the word of his servant and performeth the counsel of his messengers (Isa. 44:26).

"upon your hand": This is the left hand. You say this, but perhaps it is the right? Though there is no proof for this, it is intimated in (Isaiah 48:3) "My hand has also founded on earth, and My right hand has spanned the heavens," and (Judges 5:26) "Her hand reached for the tent pin, her right for the workmen's hammer," indicating that "hand," unqualified, is the left hand. R. Yonathan says (Devarim 6:8-9) "and you shall tie them … and you shall write them": Just as the writing (of the mezuzah) is with the right hand, so, the tying of the tefillin (on the left hand). Abba Yossi says: We find the right to be called "hand," and even though there is no proof (for its application here), it is intimated in (Genesis 48:17) "that his father placed his right hand." And what is the intent of "upon your hand"? To include an amputee (of the left hand), that his tefillin are placed on his right arm.

R. Yossi says: We find that the right hand, too, is called "hand," as it is written (Bereshith 48:17) "And Joseph saw that his father had placed his right hand on the head of Ephraim and it was wrong in his eyes, and he took hold of his father's hand to remove it, etc." (If so, how is "upon your hand" to be understood, if it can signify either right or left)? To include an amputee (of the left hand), that he places it on the right.