What was Yaakov telling Yosef? Was Yaakov telling Yosef that Yosef was to be considered his firstborn son? This is a rather backhanded way of making such a designation, as Yaakov could have said directly that Yosef would receive a double portion instead of "claiming" Efrayim and Menashe. Also, what does it mean that Yaakov "claimed" Efrayim and Menashe to be his? Was Yaakov giving Efrayim and Menashe a greater inheritance in the land of Israel than his other grandchildren? Did he have the power to distribute the land of Israel amongst his children and grandchildren?
Yaakov then recalled Rahel's death and burial, 48:7, and he went on to bless Efrayim and Menashe, 48:8-20. The chapter ends by Yaakov giving Yosef a gift, 48:21,22. Why did Yaakov recall Rahel's death and burial and why did he mention it in the middle of his blessings to Efrayim and Menashe, 48:5,6, 8-20?
One approach (see R. Saadiah Gaon on 48:7) to answering these questions is that Yaakov was adopting Efrayim and Menashe in 48:5, and then Yaakov mentioned Rahel's death to explain why he was adopting them. According to this approach, in 35:11, Yaakov was promised to have more children, but since Rahel died he was unable to have more children. Hence, here in 48:3,4, first Yaakov referred to the prophecy of 35:11, then he adopted Efrayim and Menashe to fulfill the promise of having more children, 48:5,6 and then he stated that Rahel died, 48:7.
Ibn Ezra (on 48:4) completely rejects this adoption approach. He notes that with this idea there is nothing special of Yosef's children, as Yaakov could have just as well adopted Reuven's grandchildren. Also, could adopting Efrayim and Menashe really be the fulfillment of the prophecy of 35:11 since previously they were his grandchildren? In addition, if Yaakov really felt the need to adopt his grandchildren, why did he wait until the end of this life? Or, if he felt that he had to fulfill G-d's prophecy of 35:11, why did Rahel's death stop him from having other children? If Yaakov's other wives were too old to have children, then he could have married a younger wife. Also, why did Yaakov refer to Rahel's burial in 48:7, if the whole importance of the verse according to R. Saadiah Gaon is that she died but not where she was buried? Furthermore, if Yaakov was trying to explain his action of adopting Efrayim and Menashe he should have mentioned Rahel's death in conjunction with his reference to G-d's prophecy in 48:3,4 and not after he adopted the children. Another problem is that 48:6 uses the word, their brothers, and is apparently in reference to the relationship between Efrayim and Menashe and other possible sons of Yosef, but if Yaakov really adopted Efrayim and Menashe, then they would not be brothers with Yosef's other sons. Finally, Yaakov supposedly adopted them in 48:5,6 but he did not even know that they were in the room with him! Yaakov was only told that Yosef came to see him, 48:2, and when he first saw Efrayim and Menashe, 48:8, he asked who are they? If he really had wanted to adopt his grandchildren he should have checked that they were next to him. I doubt this adoption approach, and the simple explanation of 35:11 is that G-d was promising that Yaakov would have many descendents but not that he personally was to have more children.
A second approach to explaining 48:5 is that Yaakov was attempting to educate Efrayim, Menashe and Yosef about the importance of the land of Israel. (I first heard this idea from David Silber in a lecture, and subsequently read similar ideas in articles by Mordechai Berger, 1989, and David Henshke, 1998.) With this approach, in 48;3,4,Yaakov recalled G-d's promise of 35:11,12 to stress that G-d gave the land of Israel to Yaakov and his descendants. Thus, Yaakov added the words achuzzat olam in 48:4, that the land would be an everlasting possession when he recalled G-d's prophecy, though this phrase was not mentioned in 35:12, see N. Leibowitz, 1976, p. 537. In 48:5, Yaakov was claiming that Efrayim and Menashe were his as a way to increase their connection to the land of Israel. This "claim" was not to adopt them but to confer on them special inheritance rights within the land of Israel. Yaakov was not giving them more land since the land was to be divided equally according to the population, (see Rashi on 48:6, and Bemidbar 26:52-56), but he stated that their land would be called under their names, which would give them a connection to the land of Israel. Yaakov then reminded Yosef of his mother's burial plot in order that Yosef would feel a greater connection with the land of Israel.
This approach is nice, but if Yaakov was trying to educate Efrayim and Menashe, then one would think that Yaakov would have made sure that they were present when he gave them their special inheritance rights in the land of Israel. However, again from Yaakov's question in 48:8, "Who are they?" we see that when Yaakov stated the verses 48:5,6, he thought he was speaking only to Yosef. Also, when Yaakov "claimed" Efrayim and Menashe, he made a distinction between those children who were born before he came to Egypt and those who came afterwards, 48:5. Why should there be this distinction if the goal was to increase the ties of the next generation with the land of Israel? Why not give all the children of Yosef special inheritance rights in the land of Israel? Finally, why did Yaakov wait until his final breaths to try to educate Efrayim, Menashe and Yosef about the land of Israel? Did he think the lesson would be more effective on his death bed?
A third approach to understanding 48:5,6 is that possibly there was still some tension between Yaakov and Yosef due to Yosef's absence from the home for 22 years. Maybe in his last days, Yaakov was trying to resolve an issue that he had with Yosef concerning Yosef's children. With regard to all of his other grandchildren, Yaakov had been with them when they were born and grown up, but Yaakov was not with Efrayim and Menashe when they were born and during their early years. Thus, maybe Yosef thought that Yaakov had less of a connection with them than his other grandchildren, and this could be why Yosef brought them with him when he went to see Yaakov. Yaakov, not knowing that Efrayim and Menashe were with Yosef, said that Efrayim and Menashe were his, which was his way of telling Yosef that he loved them equally to his own children, and to show that this was not an empty statement, he stated that they would have special inheritance rights, that their land would be called under their name. Yaakov did not have to make this declaration to Efrayim and Menashe since the issue was between Yaakov and Yosef. With this approach, 48:3,4, the recollection of G-d's promise to Yaakov of land was an introduction to 48:5,6.
Why then did Yaakov refer to Rahel's death in 48:7? One possibility is that Yaakov had just intended to give the blessing of 48:5,6 and then he wanted to give Yosef a gift of land in the land of Canaan, 48:21,22. 48:7 was then a lead in to 48:21,22 and it was not connected with the verses 48:8-20. Maybe 48:7 was lead in to 48:21,22 since the gift of land was to be Yosef's burial plot, and then Yaakov was explaining that just like your mother had a unique burial site so too you will have a unique burial site. Or, following the education approach, Yaakov mentioned Rahel's burial plot to increase Yosef's connection to the land of Israel through his mother. Or, following the idea that Yaakov was trying to as heal any grudges before he died, Yaakov was telling Yosef not to be mad at him for not burying Rahel in the family plot in the cave of Makhpela, see comments of Rashi, Ibn Ezra, Rashbam, Hizkuni and Radak, all on 48:7.
Berger, Mordechai, 1989, On the blessings to Efrayim and Menashe, Rinat Yitzhak, pp. 100-105.
Henshke, David, 1998, "What is the connection between the burial of Rahel and Yaakov's testament?" in Me-perot ha-ilan al parashat ha-shavuat, edited by Yehoshua Sharwtz and David Algabish, Tel Aviv: University Bar Ilan Press, pp. 146,147.
Leibowitz, Nehama (1905-1997), 1976, Studies in Bereshit, translated by Aryeh Newman, Jerusalem: The World Zionist Organization.