These were the sons of Reuben the firstborn of Israel. Though he was the firstborn, his birthright was given to the sons of Joseph son of Israel, because Reuben defiled his father’s bed. So he is not reckoned according to birthright. And though Judah prevailed over his brothers and a ruler came from him, the birthright belonged to Joseph.
And Joseph took both of them—with Ephraim in his right hand toward Israel's left hand, and Manasseh in his left hand toward Israel's right hand—and brought them close to him. But Israel stretched out his right hand and put it on the head of Ephraim, the younger; and crossing his hands, he put his left on Manasseh's head, although Manasseh was the firstborn. Then he blessed Joseph and said: "May the God before whom my fathers Abraham and Isaac walked, the God who has been my shepherd all my life to this day, the angel who has redeemed me from all harm—may He bless these boys. And may they be called by my name and the names of my fathers Abraham and Isaac, and may they grow into a multitude upon the earth." When Joseph saw that his father had placed his right hand on Ephraim's head, he was displeased and took his father's hand to move it from Ephraim's head to Manasseh's. "Not so, my father!" Joseph said. "This one is the firstborn; put your right hand on his head." But his father refused. "I know, my son, I know!" he said. "He too shall become a people, and he too shall be great; nevertheless, his younger brother shall be greater than he, and his offspring shall become a multitude of nations." So that day Jacob blessed them and said: "By you shall Israel pronounce this blessing: 'May God make you like Ephraim and Manasseh.'" So he put Ephraim before Manasseh.
Significance
Genesis 48:13-20 narrates Jacob's deliberate crossing of his hands to place his right hand on Ephraim (the younger) rather than Manasseh (the firstborn), transferring the double-portion בְּכֹרָה (bekhorah, "birthright") blessing to Joseph's sons. 1 Chronicles 5:1-2 provides the interpretive key to this event: "Though he was the firstborn, his birthright was given to the sons of Joseph son of Israel, because Reuben defiled his father's bed." The Chronicler explicitly connects Jacob's crossed-hands blessing of Ephraim and Manasseh with Reuben's forfeiture of firstborn rights (Gen 35:22), clarifying that the double portion went to Joseph while the royal preeminence went to Judah: "though Judah prevailed over his brothers and a ruler came from him, the birthright belonged to Joseph" (5:2). This passage uniquely explains why leadership and inheritance were split between two tribes.