Vayechi: blessings/curses at the deathbed

Read Genesis 49:1-28 - Deathbed blessings of the sons of Jacob

The midrash (Tanhuma Vayechi 10) reads the word ‘vayikra’ “calls” as a ‘calling out in anguish’ to God for help based on the verse in Tehilim 57:4 “I will cry to God most high: to God who performs all things for me.”
Commenting on this midrash the Mei HaShiloach says that Ya’akov is anxiety ridden because he desires to bless his sons, but he was uncertain whether he should, given their terrible behavior regarding the selling of Joseph into slavery. For this reason Jacob Avinu “cried out” ‘vayikra’ to God, turning his heart to God in surrender and asking that God place words in his mouth, for he himself is at a loss. Jacob
beseeches God to help him complete his fateful task.

And Rava bar Meḥasseya said that Rav Ḥama bar Gurya said that Rav said: A person should never distinguish one of his sons from among the other sons by giving him preferential treatment. As, due to the weight of two sela of fine wool [meilat] that Jacob gave to Joseph, beyond what he gave the rest of his sons, in making him the striped coat, his brothers became jealous of him and the matter unfolded and our ancestors descended to Egypt. (B. Talmud Shabbat 10b)

Is it indeed a blessing? On this, Ibn Ezra says, "Those who say that they are blessings, are mistaken... Where is the blessing in what was said to Reuben, Simeon and Levi?" Abravanel explains the purpose of Jacob's words as follows: "Not meant to be a blessing, nor meant to be a reproach, nor to foretell the future... but to say whether or not they were worthy of having sovereignty and dominion." Blessing or otherwise, there are three undisputed components in Jacob's testament: a call for unity, grant of the birthright, and appointment of a leader.

Reuben should have received three portions in excess of his brothers — the birthright, priesthood, and royalty. But when Reuben sinned, the birthright was transferred to Joseph, the priesthood to Levi, and the royalty to Judah. (bereishit rabbah)

Jacob takes leave of his sons with trenchant words, some positive, some negative. Earlier (48:5,20), he had already parted with Menashe and Ephraim, sons of Yoseph, elevating their status: ‘Ephraim and Menashe shall be to me as Reuven and Shimon’ (v. 5). Three imperative verbs appear at the beginning of his words, the final one repeated: ‘And Jacob called his sons and said, “Gather round that I may tell you what shall befall you in the days to come. Assemble and hearken, O Jacob’s sons, and hearken to Israel your father’ (Bereishit 49:1-2). What is the nature of this verb-laden call?
RaSHBaH (Gaon of Sura, died 1013)suggests that the three terms of command are intended to call the reader’s attention to the fact that in Jacob's address were three categories which serve as a basis for different contents: rebuke, foreseeing the future, and blessings. He considered this differentiation to be critical, for one who does not properly identify the category is liable to miss the content of the words and their meaning. (Nahem Ilan)

Isaac Abravanel suggests four possible options as to the purpose of Jacob’s “living will”. Either (i) he is offering a blessing, or (ii) moral teachings and rebuke for past wrongs. He might be (iii) offering a prediction of future events or possibly (iv) telling them of their future inheritance in the Promised Land.
These “blessings” do have a single focus. They are aimed at laying a most deliberate stress on the DIFFERENCES between the brothers. This is because Jacob is searching for the individual who is most suitable for the future leadership of the Jewish people.“As to the purpose of these statements and blessings. I think that Jacob, at the time of his death, wanted to explain and clarify from which of his children would emerge the future leadership and government of his descendents. He realised and saw through prophecy that his children would form a large collective and they would need a leader or a king, a governor of some sort. At the time of his death, Jacob wished to clarify from where the leadership and monarchy would come in order that the nation should not descend into conflict and argument over the appointment of a leader.
To this end he performed a review and an analysis of each and every one of his sons, their personality, traits and talents to determine who was most fit for the leadership ... for the nature of children...will be a product of the basic pattern set by their ancestor.. It was for this reason that he mentions here, son by son; with some, his character traits, with others, future events which will occur to his descendants. This is not for blessing, nor is it for moral correction, nor to tell the future ... It is to explain and inform who will be fitting for leadership and high office.” (Isaac Abravanel d1508 Venice)

All the blessings lend expression to the differences and uniqueness of Jacob's sons and Jacob's household. Each and every one of Jacob's sons had a unique personality, and often there were substantial contrasts between them. Judaism comprises any number of diametrically opposing elements which are united in the form of the generality of the Jewish people, in which all the unique qualities of the sons of Jacob come together in harmony... The unity is comprised of all the various spiritual strengths of the tribes of the house of Jacob. ( Rabbi J.B. Soloveitchik, Divrei Hashkafah)

(1) וזאת אשר דבר להם אביהם ויברך אתם AND THIS IS IT THAT THEIR FATHER SPOKE TO THEM WHEN HE BLESSED THEM — But were there not some of his sons whom he did not bless but whom, on the contrary, he reproached? But this is the explanation of these words: and this is it that their father spoke to them, viz., all that has been said above in this chapter, whether it be blessing or reproach. You might therefore think that he did not bless Reuben, Simeon and Levi at all — Scripture therefore states, “and he blessed them” (i.e. the 12 tribes alluded to at the beginning of the verse) which implies all of them. (Pesikta Rabbati 7). (2) EVERY MAN ACCORDING TO HIS BLESSING — according to the blessing that was to come in future to each and every one. (3) ברך אתם HE BLESSED THEM — It should have said, “every man according to his blessing he blessed him”; why, then does it say “he blessed them”? But since in the blessings he ascribed to Judah personally “the strength of a lion”, to Benjamin “the rapacity of a wolf” and to Naphtali “the swiftness of a hind”, one might think that he did not include all of them in all the blessings, Scripture therefore states “he blessed them” (i.e. each of them personally and all of them together — extending all the personal blessings to each of them) (Midrash Tanchuma, Vayechi 16; ) Rashi on Genesis 49:28