Jamieson, Fausset and Brown on Jeremiah 38:7

7. Ebed-melech--The Hebrew designation given this Ethiopian, meaning "king's servant." Already, even at this early time, God wished to show what good reason there was for calling the Gentiles to salvation. An Ethiopian stranger saves the prophet whom his own countrymen, the Jews, tried to destroy. So the Gentiles believed in Christ whom the Jews crucified, and Ethiopians were among the earliest converts (Ac 2:10, 41; 8:27-39). Ebed-melech probably was keeper of the royal harem, and so had private access to the king. The eunuchs over harems in the present day are mostly from Nubia or Abyssinia.