Adam Clarke on Leviticus 25:43

Thou shalt not rule over him with rigor - What is rigorous service? "Service which is not determined, and service whereof there is no need." This is the definition given by the Jews; but much more is implied in this command than is expressed here. Labour beyond the person's strength, or labor too long continued, or in unhealthy or uncomfortable places and circumstances, or without sufficient food, etc., is labor exacted with rigour, and consequently inhuman; and this law is made, not for the Mosaic dispensation and the Jewish people, but for every dispensation and for every people under heaven.