The Bible tells us that Rebecca was barren, so both she and her husband Isaac prayed to God for children. "And God accepted his prayer," says the Torah, "and his wife Rebecca became pregnant." The rabbis notice the nuance that it was Isaac's prayer that was excepted, not Rebecca's. In order to explain this seeming inequality, as Rebecca was a greatly righteous woman, the rabbis inform us that the prayer of a Tsaddik (righteous person) the son of a Tsaddik is more powerful than that of a Tsaddik the son of a rasha (evil person).
This, however, still seems to be quite unfair. If a person is righteous, what difference does it make what his parents were? Why should his prayer is not be as readily accepted?
I don't believe that this rule applies in every case. In the case of children, however, it very well may apply. After all, if the person praying is a Tsaddik the son of a Tsaddik, the odds are that the child will also be a Tsaddik. A pattern has been established. But if the Tsaddik is the son or daughter of a rasha, there's no guarantee what the child will choose for his life path. So, in this area, there is logic to accepting the prayer of a Tsaddik the son of the Tsaddik for children.
Indeed, Rebecca had twins. Their similarity, however, ended with the fact that they were born more or less together. Esav was a hunter, a man who functioned on the basis of violence and fighting. Jacob was a simple scholarly boy who "dwelled in the tents." Interestingly, it was Esav whom Isaac loved "because he was a hunter, in his parlance," while Rebecca loved Jacob. How did this come to be?
I believe the psychology here is very potent. First of all, it would seem that Esav came more from Rebecca's side of the family. How so? Both her father and her brother were deeply dishonest characters. About Laban, the brother, we will read much in the next sections of the Torah. His attempts to cheat and, ultimately, harm Jacob are clearly recorded. As for her father, Betuel, the Rabbis claim he sought to torpedo the match of Rebecca and Isaac by poisoning Eliezer, Abraham's servant, who had come to arrange that match.
The fact that Rebecca remained righteous in such a negative environment is a huge testimony to her tremendous spirituality. (Apparently it ran in the women of the family, as Laban's daughters, Rachel and Leah, were similarly righteous.) Nonetheless, in order for her to maintain her spirituality, she had to constantly be on guard against the influences of her own family. In her own way, she had to fight back. Esav, clearly, was an extreme expression of that "fighting back." He took no garbage from anyone, and often initiated the violence.
Jacob, on the other hand, was clearly the son of Isaac and the grandson of Abraham. He was, simply, a good boy. That makes sense, because Isaac grew up in an environment of goodness and kindness. The one possible negative influence, Ishmael, had been sent away by his perceptive mother when he was still young.
Isaac suffered anti-Semitism. He was not a fighter, and he was taken advantage of. The story of the wells that he dug, some of which were from the time of his father Abraham, illustrates this. Each time he dug or cleared such a well, the Philistines came and filled it with dirt. They contested every well he dug, every place he settled. Only when he had distanced himself sufficiently did the Philistines leave him alone.
I suspect that this is what attracted Isaac to Rebecca, and what made him love her son Esav. He saw in Rebecca a woman who could hold her own against hostile others. He saw that even more in Esav. He knew that this was a weakness of his, and these dear people made him complete.
On the flipside, Rebecca yearned for the pureness and innocence that she saw in Isaac. Growing up in a home of crooked people, she deeply needed to experience a world of goodness. She saw that in Isaac, and even more so in their son, Jacob.
In the end, Rebecca won the battle. At her urging, Jacob used deception to secure the blessing of his father Isaac. And when Isaac realize what happened, he confirmed that blessing. At that moment, the true nature of his boys became apparent to him.
One wonders how and Esav could come out of a Rebecca and Isaac! The answer is, Esav was not intrinsically evil! He did, however, make one fatal flaw in his choice of a path in life. He chose to live reactively, and to see others as his main obstacle. He allowed the hostility of others to define himself.
Jacob, on the other hand, chose to set his own agenda. He was not afraid of the world, but he refused to let the world define who he would be. He was born into a home of goodness and kindness. He believed in a beautiful world, and he set about to live his life in such a world. Wherever and whenever that world didn't cooperate, he was capable of coping with it. That, he inherited from his mother. Not only inherited, but he learned it from her as well. When she instructed him to bring the meat into his father and claimed to be Esav, she was teaching him to not be passive in the face of wrongdoing.
But, at the end of the day, Jacob lived his life for the beauty of the world of the beauty of tradition. That, and only that, was how he defined himself, and the people he begat.