Bereishis, 48:17-19: “Yosef saw that his father was placing his right hand on Ephraim’s head and it displeased him, so he supported his father’s hand to remove it from upon Ephraim’s head to Menashe’s head. And Yosef said to his father, ‘Not so, father, for this is the firstborn; place your right hand on his head. But his father refused, saying, “I know my son, I know; he too will become a people and he too will become great; yet his younger brother will become greater than he, and his offspring’s [fame] will fill the nations.”
Bereishis, 49:28: “All these are the tribes of Israel – twelve – and this is what their father spoke to them and he blessed them; each according to his appropriate blessing he blessed him.”
Rashi, Bereishis, 49:28, Dh: According to his appropriate blessing: “The blessing that in the future will come upon each one.”
A recurrent theme in Parshas Vayechi is that of blessings. The early part of the Parsha covers Yaakov blessing Yosef’s two sons and later, the Torah relates Yaakov’s blessings to all his sons before his death. A close analysis of certain aspects of these accounts can help us attain a deeper understanding of the purpose and significance of blessings, which we will see is a much-misunderstood concept.
When Yaakov came to bless Yosef’s sons, Menashe and Ephraim, Yosef expected him to place his stronger right hand on the elder Menashe and to give him the blessing suitable for the first-born. However, Yaakov placed his right hand on the younger Ephraim. When Yosef tried to correct him, explaining that Menashe was the first-born, Yaakov asserted that he was aware of that, but Ephraim was destined to have greater offspring, therefore he should merit the greater blessing. The question arises as to what exactly was the nature of the ‘machlokes’ between Yaakov and Yosef. In addition, as Rav Yerucham Levovits points out, it is not immediately apparent how Yaakov answered Yosef’s argument. Yosef was claiming that since Menashe was the older one, he deserved the blessing that goes to the bechor. Yaakov answered that Ephraim would be greater than Menashe, but why does that dictate that Menashe should not get the blessing of the bechor?
This can be answered by explaining an enigmatic statement by Rashi at the end of the section of the blessings that Yaakov gave to his sons. The verse states that he blessed each one according to his appropriate blessing. The exact meaning of this is unclear – Rashi explains that it refers to the blessing that in the future will come upon each one. Rashi’s explanation also needs clarification. This can be explained with a yesod of Rav Levovits about blessings. He notes that people often make a mistake when they go to a Tzaddik for a blessing. They think that he has a box full of blessings and they ask him to give him one of the blessings from his box. But we know that a blessing can only serve to add to what a person already has. For example, in the case of the miracle when Elisha blessed the oil of Ovadiah’s wife, he requested something already extant that the blessing could be activated upon. The same idea applies to giving a person a blessing for success in a certain area. If he has no potential in that area, then the blessing is pointless.
Rav Yissachar Frand shlit’a gives an analogy to help make this idea tangible. “There is plant food. There is a plant food that is custom made for roses. When a person applies these nutrients to a rose bush, one will be able to grow lush and beautiful roses. If a person uses the same plant food (designed for roses) on daffodils, it is not going to work because this food is only designed to bring out “rose potential”, not “daffodil potential”. Likewise, explains Rav Frand, “If someone does not have a good voice and he goes to a Tzaddik and says, “I want to be a world class chazzan like Helfgot” he should not expect miracles. No Tzaddik can give a bracha to make a person who cannot carry a tune into a world-class chazzan.”
This, then, is what it means when it says Yaakov blessed his sons, each according to his blessing he blessed them and when Rashi refers to the blessing that will come upon him in the future. He only expressed the blessings that each one was destined to already potentially have within themselves. It would not work to give Zevulun the blessing that he should become a Yissachar or vice versa. The purpose of a blessing is that the recipient should become what he already potentially is destined to become, it is not a magic potion that can create something from nothing.
We can now understand the back and forth between Yaakov and Yosef during the blessings of Ephraim and Menashe. Yosef looked at his two sons and argued that Menashe, as the first-born, should get the predominant blessing. Yaakov replied, ‘I know my son, I know’, meaning that he knew through Ruach HaKodesh something that Yosef didn’t know. That despite their birth order, Ephraim would be the greater of the two, and thus he needs the predominant blessing the enable him to reach his potential. It would simply not work to try to give that blessing to Menashe. Yosef himself was aware of how blessing works, but he naturally assumed that since Menashe was the first-born, he would automatically have greater potential, but he did not have the prophetic vision of Yaakov that showed otherwise.
The lesson that can be derived from Rav Yerucham’s yesod is that blessings do not work like ‘magic’ in that a person can go to a Gadol and get a blessing on whatever he wants. A blessing can only be effective when it builds on what is already extant. So, for example, if a person wants a blessing to become a Talmid Chacham, it has no chance of working, if he does not make the requisite effort in his learning. Rav Yerucham also points out that when people came to the Chofetz Chaim for blessings he would often tell them that learning Torah would be more of a blessing. Rav Yerucham explains that he wasn’t merely pushing them away, rather he was saying that Torah was the ultimate source of blessing, so why not directly access that. May we all merit to be vessels to receive blessings in all areas.
 Daas Torah, Vayechi, p.274.
 Melachim Beis, 4:2.
 A famous Chazzan.