Albert Barnes Commentary Exodus 21:2

"If thou buy a Hebrew servant, six years he shall serve: and in the seventh he shall go out free for nothing." — Exodus 21:2 (ASV)

A Hebrew might be sold as a bondservant in consequence of either debt (Leviticus 25:39) or of committing theft (Exodus 22:3). But his servitude could not be enforced for more than six full years. Compare the marginal references.