Isaac was old and near death. He asked his oldest son Esau to go out into the country and kill some wild game and to fix for him a tasty meal. Rebekah overheard this and after Esau left, she plotted with Jacob to trick Isaac into giving his blessing to Jacob instead of Esau. When Esau returned, he realized that Jacob had stollen Isaac's blessing. He asked his father to fix the situation but Isaac stood with his word. Thus Esau was to be subserviant to Jacob and hated his brother for this deception.
Jacob believes God wants him to have the birthright and will justify a sinful lie in the pursuit of the birthright, saying he is standing for righteousness. It seems to have been missed in all this intrigue that blessings come from God and not man. It is as if God intended this path to come about, but Esau fell for it.