The Torah says the Hebrew maid-servant "shall go out free" if her master fails to fulfill his obligations (Exodus 21:11). The Mekhilta probes the meaning of the word "free" with a question that has significant legal consequences. Does "free" mean free from everything, including the requirement of a divorce document?
Consider the scenario. The master has designated the maid-servant as his wife or his son's wife. A marriage has taken place. Now the relationship has broken down, or the obligations have not been met. She "goes out free." Does this mean she walks away without needing a get, a formal bill of divorce? If so, she is an exception to the general rule that requires every married woman to receive a get before she can remarry.
The Mekhilta initially entertains this possibility. Perhaps the maid-servant's "freedom" is total, encompassing both the financial and the documentary aspects of dissolution. If this were true, then (Deuteronomy 24:1), which commands "then he shall write her a bill of divorce," would apply to all other women but not to a Hebrew maid-servant.
The Mekhilta rejects this reading. "She shall go out free" means free of money. No payment is required for her release. She does not need to buy her freedom, and no one needs to pay the master for her departure. But she is not free of a get. If she was married, she still requires a proper bill of divorce before she can remarry.
The distinction between financial freedom and documentary freedom matters. A woman who leaves a marriage without a get remains legally married. The Torah's grant of "freedom" to the maid-servant addresses the economics of her situation, not the formalities of her marital status. She leaves without paying, but she does not leave without proper legal dissolution.