Despite the permanence of Canaanite servitude, there was one path to freedom that did not require the master's consent: suffering. If a master persecuted his Canaanite bondservant and knocked out a tooth, blinded an eye, or maimed any external organ, the bondservant "acquires himself" — wins his own freedom — through his afflictions.
The Mekhilta then constructs a powerful a fortiori argument. If a bondservant can acquire his freedom through afflictions inflicted by a human master — mere "flesh and blood" — how much more so can afflictions imposed by Heaven lead to spiritual liberation! If human cruelty can break the chains of servitude, surely divine discipline can accomplish something even greater.
The proof text is (Psalms 118:18): "The Lord has afflicted me exceedingly, and He did not consign me to death." The Psalmist endured terrible suffering but emerged alive. The suffering was not punitive destruction — it was transformative. It purchased something.
This teaching bridges civil law and theology in a way characteristic of the Mekhilta. A specific legal ruling about bondservant emancipation becomes the foundation for a universal spiritual principle. Suffering has redemptive power. Physical affliction, whether imposed by a human hand or by divine providence, can be the mechanism through which a person is freed — freed from servitude, freed from sin, freed from the limitations of their prior condition. Pain is a price, and it buys liberty.