When a Hebrew bondsman is released after six years, the Torah says "he shall go out to freedom." The Mekhilta asks: what does this phrase add? If the bondsman's term is over, he is obviously free. Why state the obvious?
The answer addresses a potential legal complication. (Deuteronomy 15:13) says: "And when you send him away free, you shall not send him empty-handed." From this, one might think that "sending away" requires a formal legal document — a writ of emancipation — similar to the bill of divorce required when ending a marriage. Perhaps the bondsman's freedom is not effective until his master provides written proof.
The Torah preempts this by saying "he shall go out to freedom." The word "freedom" operates automatically. No document is required. When the sixth year ends, the bondsman walks out. His freedom is self-executing.
The Mekhilta then considers another possibility. Perhaps the bondsman must compensate his master for the release — pay some kind of exit fee. The Torah blocks this too: "he shall go out to freedom, gratis." The word "gratis" — chinam in Hebrew — means the bondsman owes nothing. He does not buy his way out. He does not negotiate a settlement. He simply leaves, owing nothing, carrying whatever gifts his master is required to provide. Freedom in Jewish law is not purchased. It arrives on schedule, costs nothing, and requires no paperwork.