(21:1) These are the laws that you must set before them.
that you must set before them From where do we know that a teacher should explain the reasons of the laws to his students and not teach in an authoritarian way? From “These are the laws that you must set before them” so that they can be easily understood, rather than teach by rote (Eruvin 54b).
(21:2) If you buy a Hebrew slave—one that was sold for robbery—he shall serve for six years, but in the seventh year he shall go free, for no charge.
He shall serve for six years How do we know that a runaway slave must make up the full six years of service? From “He shall serve six years.” I might think that he must make up the years even if he was sick during the period; that's why it says “but in the seventh year he shall go free.” He goes free, even if he was sick during his term of service (Kiddushin 17a).
free, for no charge Even if he was sick and his master incurred great expense because of him, he owes nothing; for it says “He