His servant, namely, a stranger; for an Israelite was to be better used. See Lev_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.