The struggle between Jacob and Esau that began in their mother's womb symbolizes the contest between the twin realities within each of us.
This is a never-ending struggle, in which "one nation" attempts to "prevail over the other" and in which a greater exertion on the part of one meets a corresponding effort by its adversary.
Even when one side overpowers the other, that can never produce a fundamental change, a banishment from one's soul.
It is the conflict between Edom and Israel, two opposite realities, that will conclude only at the end of days.
Hasidim tell a story that, behind the humor, offers an important lesson.
The Midrash relates that Rebecca felt a wrestling match taking place in her womb when she was pregnant.
Whenever she passed the entrance to the study hall, Jacob tried to come out; when she passed the doorway of a place of idolatry, Esau pushed hard to exit.
Rebecca sought counsel from God; she feared that the one attempting to go to the study hall was the same one rushing to idolatry.
When God answered her, "Two nations are in your womb,” she sighed in relief.
The awareness of two opposing forces clashing in our consciousness is no major cause for concern.
True, it would unhinge us if we thought that the internal strife that we feel springs from a single source, a single soul.
One's spirits would fall whenever the evil inclination exposed itself.
While you are in the middle of prayer surrounded by an aura of holiness, a dozen of the worst thoughts imaginable arise.
You are performing a commandment, and immediately afterward you fall into a devastating mood from which escape seems impossible.
If a person believes that he has only one soul (the soul that prays in holiness is the same one contemplating destructive thoughts), he will lose all hope.
Am I even human? he might well ask himself.
Will I ever be human?
But when he knows that "Two nations are in your womb,” that not one but two souls are struggling inside and that "one nation shall prevail over the other,” when he realizes that he stands in the middle of a struggle that by definition cannot reach a resolution, then the ups and downs take on a different significance in this inner battle.
Then he understands that he has the capacity to perceive the holy, while being utterly unaware of the other side's existence.
And still he must be cognizant that the other side is alive and well.
He must know, in addition, that evil can manifest itself within him to such an extent that he forgets the experience of holiness.
Nevertheless, he must keep in mind that holiness is there, inside, and that he need merely uncover it.
–Rabbi Adin Steinsaltz
From Learning from the Tanya by Rabbi Adin Steinsaltz