One of the most difficult to understand things in the Torah for most people remains the blessings of Yitzchak. Why did Yitzchak favor the wicked son with the blessings and why was Yaakov's only resort to trick his father. It's an understandable question when looking back retrospectively but it is important to remember that we are dealing with people who could not look back, only forward speculatively.
What baffles most people, Yitzchak's selection of Esav, becomes significantly less so when we look at it in the context of the time and place. Yitzchak was a son of Avraham but lacked his status or strength. The parsha is called Toldos Yitzchak but the only material involving Yitzchak it relates to us up until the blessings are his travails at the hands of the Phlistim. Like Avraham, Yitzchak found himself a wanderer and an alien among peoples who were all too willing to take advantage of him. Indeed both Avraham and Yitzchak even found themselves having to claim their wives as their sisters for survival's sake.
Next we have a description of his two sons. Esav who is a hunter and Yaakov who is a quiet peaceful man who sits and learns in a tent. In a cruel world, when Yitzchak knew whoever succeeded him would have to build a family and a nation, survive centuries of enslavement in Egypt and then build a kingdom; the choice was obvious. Esav. Esav had the strength that the difficult times ahead would require, Yaakov by contrast is obedient and dutiful, which were virtuous qualities and key to a relationship with G-d but would leave him vulnerable and weak when dealing with men.
Still both Yaakov and Esav represented unhealthy extremes. What Yitzchak wanted was a middle ground, Esav's strength and Yaakov's righteousness. The blessings were a test. Sending Esav out to demonstrate the righteousness that had been innate in Avraham's house by showing hospitality to his father while leaving Yaakov no choice but to take desperate measures to gain the blessings. Thus one son or the other would have to demonstrate that he could take on enough of the attributes of the other to be worthy.
When Yitzchak says, "HaKol Kol Yaakov, Ve'HaYadaim Yedei Esav", "The Voice is the Voice of Yaakov but the Hands are the Hands of Esav", he is saying it appreciatively recognizing that Esav has taken on some of the attributes of Yaakov. When it instead proves that Yaakov took on some of the attributes of Esav by tricking him, Yitzchak affirms that he is still blessed. By showing that he could do what has to be done, Yaakov showed his fitness to be the one to build the chosen nation that would come. It is only after this test of the blessings, that the blessings of Avraham are given with the same prerequisite that had been placed before Eliezer, which was that whoever inherits the blessings of Avraham cannot marry a Caananite. This was not an issue up till now because the blessings of Avraham had not yet been given to either son.
An obvious question that comes to most people's minds is why all this is required. After all it is G-d who decided that Yitzchak was chosen and Yishmael was not, not Avraham. Similarly it should have been G-d who made that distinction between Yaakov and Esav. And indeed it was. The prophecy at the beginning of Parshat Toldos had Hashem informing Rivka of the nature of her sons and the eventual outcome. Yet throughout the actual events, Hashem seemed to be hidden and allowing events to play out as they did.
Why? God's will and promise may prophesize that a man will receive something but not properly prepare him to receive it. Despite the prophecies of the Exodus and the Kingdom of Israel, the people all too often did not manage to live up to the prophecies themselves. It requires a physical and spiritual journey for a man to be ready to live up to what is given to him. Such a journey was required of Yaakov. Had he simply received the blessings and remained in his parent's home, had he been the first born all along, he would not have been prepared to deal with the hardships and suffering that he and his sons and his people would have to endure. Instead he had to struggle and learn to compete in an unfair world, rather than sit and learn in a tent. He had to make his way with no support beyond G-d and leave a legacy of learning to survive in exile.
When he encountered Lavan, who tricked him into marrying Leah who had been intended for Esav, he was was tricked into accepting Esav's intended wife as he had tricked Esav out of his birthright. Life was not going to be the way he wanted it to be. By marrying Leah, Yaakov was performing a kind of Yibum. In Yibum, where a brother marries a deceased brother's wife in order to perpetuate his brother's name, we believe that the children are in a sense his brother's. By marrying Leah, Esav who was spiritually deceased, became perpetuated as well. And the children of Leah proved to have the righteousness of Yaakov but also the strength of Esav to cope with a hostile world.
When Dina was kidnapped, for the first time the cycle of the Avot is broken and instead of accepting when Sara and Rivka were threatened by claiming them as sisters, Shimon and Levi actually go out and slaughter her kidnappers. Yaakov mourns and castigates them but it is a demonstration of the strength of Esav that is required to deal with a dangerous threatening world. When fused with righteousness, it is that strength that produces the Leviim who assemble at Moshe's side swords drawn and Pinchas who seizes a spear and acts zealously in G-d's name. A peaceful man who sits in tents could not do this. Yitzchak was right in that it takes a middle ground between Esav and Yaakov that was created when Yaakov married Esav's intended bride.
It was the distant descendant of his, King David, who is described as being ruddy like Esav and having a similar personality to Esav, who would build the kingdom of David. Who would fuse Esav's skill at violence with Yaakov's facility with prayer. If as the Gemara says, every answered prayer comes from someone who is descended from Yaakov and every military victory from someone who is descended from Esav, the Jewish people had to have both to survive and did.
This is the wisdom of Yitzchak that most overlook when they regard his choice of Esav as blindness. Yitzchak may have been blind but he saw beyond the merely physical and the nature of his sons as it was now, looking into the future at the demands that time and destiny would place upon them. He knew that righteousness and learning were what mattered but they were not enough to survive in this world and that righteousness without the willingness to use force would be ineffectual, would too easily devolve into pacificism. If Yaakov was reluctant to use force, his sons were not, and it is they who would carry on the blessings of Avraham and his destiny to its fulfillment.