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.

Fear thy God - Yahweh was the Lord and Master of His people. To treat a Hebrew as a slave was therefore to interfere with the rights of Yahweh. Compare Romans 14:4.

25:43 Fear thy God - Though thou dost not fear them who are in thy power, and unable to right themselves, yet fear that God who hath commanded thee to use them kindly, and who can and will avenge their cause, if thou oppress them.