The Hebrew Servant (Mitzvot 42-46 and 481-482)

Why is the law of the Eved Ivri/Amah Ivriah the bridge between Har Sinai and the Ten commandments and civil law? For most of Jewish History this hasn't even been relevant. Why is Eved Ivri so central, why didn't the Torah prohibit servitude?

Delivered at the OU Israel Center, Wednesday, October 17, 2018/8 Marcheshvan 5779