The Torah addresses the case of a father who refuses to allow his daughter's betrothal. The verse uses the phrase "if her father refuse, refuse," repeating the word in a way that immediately catches the Mekhilta's attention. This kind of repetition in the Torah is never accidental, and the Rabbis extract a legal expansion from it.
The straightforward reading of the verse covers only a woman who has a father. Her father has the authority to refuse a proposed match on her behalf, and the verse describes the exercise of that authority. But the Mekhilta asks: what about a woman whose father has died? Does she lose the right of refusal simply because the person who would normally exercise it on her behalf is no longer alive?
The answer comes from the doubled language. The verse does not say "if her father refuse" once. It says "refuse, refuse," and the Mekhilta interprets the repetition as an expansion: refusal applies "in any event." Whether the woman has a father or not, the right of refusal exists. A fatherless woman can refuse on her own behalf.
This interpretation has profound implications. It ensures that a woman's autonomy in matters of marriage is not contingent on having a living male relative to speak for her. The Torah's doubled language, read through the Mekhilta's lens, creates a legal safety net. No woman is left without recourse simply because of bereavement.
The Rabbis derived this entire principle from two words. The repetition that a casual reader might dismiss as stylistic emphasis becomes, in rabbinic hands, the foundation of a woman's independent right to refuse a marriage she does not want.