A Roman noblewoman, a matrona, came to Rabbi Yose ben Halafta with a question. She had been reading the book of Genesis, and she was curious about the birth of Rebecca's twins. "Why," she asked, "was Esau the firstborn and not Jacob? Jacob was the righteous one. Jacob carried the covenant. Surely he should have been born first."
Rabbi Yose did not argue with her reading. He gave her a midwife's answer.
"To cleanse the place," he said, "for the birth of Jacob."
The womb, in Rabbi Yose's image, was not a pure chamber. It held what we all hold in the beginning, a mixture of tissues and fluids, some of which are simply the by-products of gestation and need to be expelled. Esau came out first carrying all of that matter. His body absorbed the rougher stuff of the shared pregnancy. Once Esau had passed through, Jacob could be born into a clean passage.
The midrash is physiological in its language but theological in its point. Jacob's righteousness, the rabbis are hinting, was not accidental. Even before his birth, the world was being arranged around him. Esau had his own role to play, not as the chosen son but as the one who cleared the ground. The Exempla preserves this answer among Rabbi Yose's brief responses to matronae, the educated Roman women who enjoyed putting the sages on the spot. Bereshit Rabbah 63 records the tradition at greater length. Some people are born to stand first so that someone else can stand clean.