His servant, namely, a stranger; for an Israelite was to be better used. See Leviticus 25:39,40, &c. With a rod; a fit and usual instrument for correction, whereby it is implied, that if he killed him with a sword, or any such weapon, he was to die for it. Under his hand, i.e. whilst the master is correcting him. He shall be surely punished; not with death, for then it would have been said so, as it is before and after; but as the magistrate or judge shall think fit, according to the diversity of circumstances; and therefore no particular punishment is set down.
Related Commentaries of Exodus 21:20
Exodus 21:20
20 And if a man smite his servant, or his maid, with a rod, and he die under his hand; he shall be surely punished.e