Isaac and Rebecca had no children for the first 20 years of their marriage. When their prayers were finally answered and Rebecca conceived, she suffered intense pregnancy pain. G‑d informed her that she was pregnant with twins who would be opposites – not only physically, but morally, as well – and that each one’s success in pursuing his path in life would be at the expense of the other’s.
Double Identity
וַיֹּאמֶר ה' לָהּ שְׁנֵי גוֹיִם בְּבִטְנֵךְ וּשְׁנֵי לְאֻמִּים מִמֵּעַיִךְ יִפָּרֵדוּ וּלְאֹם מִלְאֹם יֶאֱמָץ וגו': (בראשית כה:כג)
G‑d told her, “Two nations are in your womb; two powers will diverge from within you. The upper hand will pass from one power to the other.” Genesis 25:23

Metaphorically, Jacob and Esau represent the two souls (and their opposing drives) that exist within each of us. We each possess an inner Jacob – i.e., our Divine soul with its G‑dly drives, and also an inner Esau – i.e., our animating soul with its selfish drives. When our Divine soul asserts itself, it weakens the materialistic tendencies of the animating soul.

The Divine soul overcomes the animating soul in the same way that light overcomes darkness. Light does not have to actively exert itself to dispel darkness – darkness simply ceases to exist in the presence of light. Similarly, as soon as we let the holiness and goodness of our Divine souls shine by studying the Torah and observing the commandments, the selfishness of the animating soul disappears.1