If a man has two wives, the one beloved and the one hated, and they bear him sons, the beloved and the hated, and the firstborn son is the hated one’s—
English: “The firstborn son to the hated one” — Scripture informs you that the firstborn son will be the hated wife’s.
On the daf / in context: The language is read as a prediction: the child born of the forbidden or undesired union will turn out to be the firstborn, and the father will be unable to prefer the son of the beloved wife. This continues the theme that following the yetzer hara leads to unwanted consequences.
Type of Learning
Derash on the predictive force of “ve-haya.”
What Is Learned
The Torah predicts that the firstborn will be the son of the hated wife; the father may not transfer the double portion to the son of the beloved wife.