The forefathers were “chariots”, completely devoted to G-d’s will, and so it is impossible that Eisav could be predestined from the womb to a life of sin. Eisav’s predilections were given to him by G-d so that he can model another path of Divine service for the descendants of the forefathers. Some people do not experience great challenges to their Divine service, they are not easily led astray. These unblemished souls follow the example of the forefathers' devotion.
But most people are challenged every step of the way in their Divine service, and they have to access a deep strength within their souls to overcome those obstacles. Yitzchak personified strength and courage in Divine service, and this strength is what lives in the souls of these spiritual warriors. However, Yitzchak did not actually experience the temptations and allure of the evil inclination, he had external pressures, not internal. Eisav, his son, was meant to be the first personality who could contend with the battle within by revealing the essence of his soul’s power.
Thus, Eisav received spiritual education from his father and grandfather; he was capable of overcoming his challenges. In that embryonic, and early childhood, version of Eisav, he was a “man of the field” in the sense that he was uniquely able to redeem the vigor of the field, of the material world. Regrettably, he did not fulfill this expectation and allowed his animal impulses to rule his consciousness.
