There is no doubt that Jews lived in Ethiopia at that time, and in rather significant numbers. Yet the writer does not call him a Hebrew from Ethiopia, but an Ethiopian.
"Eunuch" means a castrated man. In the East such men were, among other things, overseers of royal harems. From this office they often advanced to higher offices of state.
Moreover, eunuchs in general were sometimes appointed to high state offices. Consequently, the name "eunuch" was sometimes used of any person holding high office, even if he was not castrated.
Therefore many have supposed that here too the word "eunuch" does not properly mean a castrated man. They take it to mean a man holding high office under the queen of Ethiopia.
They support this reasoning by the fact that, according to the Law of Moses, Deut 23:1, a eunuch could not belong to the assembly of Jehovah.
Yet this eunuch traveled to Jerusalem as a pilgrim and read the prophet's book.
But if this eunuch had not been a eunuch in the strict sense, that is, a castrated man, the word would be superfluous in the text. His high office under the queen is directly mentioned afterward.
Moreover, his very position as a courtier close to the queen compels one to suppose, according to Eastern customs, that he was a eunuch in the strict sense.
According to the Law of Moses, a eunuch could not be admitted into the assembly of Jehovah. This only means that such a man could not be a full proselyte, a "proselyte of righteousness."
Such a man could be a proselyte of the second degree, a "proselyte of the gate," see note on Jn 12:20. Such, probably, was this Ethiopian eunuch.
"Courtier" is further explained by the statement that he was keeper of all the queen's treasures. Therefore he was one of the most important officials in the East, and one of those closest to the queen.
"Candace, queen of Ethiopia." Ethiopia was the name of the country lying south of Egypt, where Nubia and Abyssinia now are. Its political and commercial center was Meroe.
Even in the time of Eusebius, as in ancient times, this country was ruled by women. As in neighboring Egypt all kings were called Pharaohs, so in Ethiopia all queens were called Candaces, Pliny, Hist. natur. 6.35.
He had come to Jerusalem to worship. As a proselyte of the gate, he had access to the temple and could offer sacrifice in the temple to the true God, on equal terms with the Jews.
Probably he had been converted to the Jewish faith by one of the Jews who lived in Ethiopia in significant numbers and were always zealous in spreading their faith.