Charles Ellicott Commentary Isaiah 18:2

"that sendeth ambassadors by the sea, even in vessels of papyrus upon the waters, [saying], Go, ye swift messengers, to a nation tall and smooth, to a people terrible from their beginning onward, a nation that meteth out and treadeth down, whose land the rivers divide!" — Isaiah 18:2 (ASV)

That sends ambassadors ... —The words point to the embassies which the Ethiopian king had sent, in the papyrus boats used for the navigation of the Upper Nile, down that river to Hezekiah and other princes, inviting them to join the alliance against Assyria.

Go, you swift messengers ... —With the interpolated “saying” omitted, the words that follow are the prophet’s address to the messengers, as he sends them back to their own people. Instead of “scattered and peeled,” we are to read tall and polished, as describing the physique which had probably impressed itself on Isaiah’s mind. (Compare the Sabeans as men of stature in Isaiah 45:14.) They were terrible then, as they had always been (i.e., imperious and mighty), a nation that treads down its foes.

Instead of “meted out and trodden down,” they are a nation of command, command (or, perhaps, “strength, strength”). The rivers are literally the affluents of the Nile that intersect and fertilise (not “spoil”) the hills and valleys of Nubia. Some commentators, however, though with less probability, accept the Authorised Version, and refer the words to Israel, as “scattered and plundered,” with its land “spoiled” by the rivers of invading armies (Isaiah 8:7).