The Torah states that a master who takes a Hebrew maid-servant as his wife must provide for her "according to the ordinance of the daughters" (Exodus 21:9). The Mekhilta asks what this phrase actually teaches, and the answer it discovers is far more sweeping than the verse's immediate context might suggest.
At first glance, the phrase seems to come to teach something specific about the maid-servant. It appears to define her rights after marriage. But the Mekhilta reveals that the teaching flows in the opposite direction. The verse about the maid-servant ends up "learning" from daughters in general, while simultaneously establishing a universal rule about all Jewish daughters.
The logic works as follows. Verse 10 specifies three things that a master-turned-husband must not diminish for the maid-servant he has married: "her food, her clothing, and her conjugal time." When the Torah then says he must treat her "according to the ordinance of the daughters," it creates a bridge between the specific case and the general category. Just as this particular woman, the former maid-servant, is entitled to food, clothing, and conjugal time, so every Jewish daughter who marries is entitled to the same three things.
Rabbi Yoshiyah identifies this as the scriptural source for a husband's three fundamental obligations to his wife in Jewish law. These are not voluntary acts of generosity. They are legal requirements that a husband must fulfill, enforceable by the courts. The maid-servant's protections became the template for every Jewish marriage. What began as a law about the most vulnerable woman in society, a former servant, became the foundation of marital rights for all women in Israel.