Numbers 12:1 - Joseph Benson’s Commentary on the Old and New Testaments

And Miriam Miriam seems to be first named, because she was the first mover of the sedition; wherefore she is more eminently punished. The Ethiopian Either, 1st, Zipporah, who is here called an Ethiopian, in the Hebrew, a Cushite, because she was a Midianite: the word Cush being generally used in Scripture, not for Ethiopia, properly so called, above Egypt, but for Arabia. If she be meant, probably they did not quarrel with him for marrying her, because that was done long since, but for being swayed by her and her relations, by whom they might think he was persuaded to choose seventy rulers; by which copartnership in government they thought their authority and reputation diminished. And because they durst not accuse God, they charge Moses, his instrument, as the manner of men is. Or, 2d, Some other woman whom he married, either while Zipporah lived, or rather because she was now dead, though that, as many other things, be not recorded. For, as the quarrel seems to have been about marrying a stranger, it is probable it was a flesh occasion about which they contended. And it was lawful for him as well as any other to marry an Ethiopian or Arabian woman, provided she were a sincere proselyte.