A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
isa 20:1CONTINUATION OF THE SUBJECT OF THE NINETEENTH CHAPTER, BUT AT A LATER DATE. CAPTIVITY OF EGYPT AND ETHIOPIA. (Isa 20:1-6)
Tartan--probably the same general as was sent by Sennacherib against Hezekiah (Kg2 18:17). GESENIUS takes "Tartan" as a title.
Ashdod--called by the Greeks Azotus (Act 8:40); on the Mediterranean, one of the "five" cities of the Philistines. The taking of it was a necessary preliminary to the invasion of Egypt, to which it was the key in that quarter, the Philistines being allies of Egypt. So strongly did the Assyrians fortify it that it stood a twenty-nine years' siege, when it was retaken by the Egyptian Psammetichus.
sent--Sargon himself remained behind engaged with the PhÅnician cities, or else led the main force more directly into Egypt out of Judah [G. V. SMITH].
isa 20:2by--literally, "by the hand of" (compare Eze 3:14).
sackcloth--the loose outer garment of coarse dark hair-cloth worn by mourners (Sa2 3:31) and by prophets, fastened at the waist by a girdle (Mat 3:4; Kg2 1:8; Zac 13:4).
naked--rather, "uncovered"; he merely put off the outer sackcloth, retaining still the tunic or inner vest (Sa1 19:24; Amo 2:16; Joh 21:7); an emblem to show that Egypt should be stripped of its possessions; the very dress of Isaiah was a silent exhortation to repentance.
isa 20:3three years--Isaiah's symbolical action did not continue all this time, but at intervals, to keep it before the people's mind during that period [ROSENMULLER]. Rather, join "three years" with "sign," a three years' sign, that is, a sign that a three years' calamity would come on Egypt and Ethiopia [BARNES], (Isa 8:18). This is the only instance of a strictly symbolical act performed by Isaiah. With later prophets, as Jeremiah and Ezekiel, such acts were common. In some cases they were performed, not literally, but only in prophetic vision.
wonder--rather, "omen"; conveying a threat as to the future [G. V. SMITH].
upon--in reference to, against.
isa 20:4buttocks uncovered--BELZONI says that captives are found represented thus on Egyptian monuments (Isa 47:2-3; Nah 3:5, Nah 3:8-9), where as here, Egypt and Ethiopia are mentioned as in alliance.
isa 20:5they--the Philistine allies of Egypt who trusted in it for help against Assyria. A warning to the party among the Jews, who, though Judah was then the subordinate ally of Assyria, were looking to Egypt as a preferable ally (Isa 30:7). Ethiopia was their "expectation"; for Palestine had not yet obtained, but hoped for alliance with it. Egypt was their "glory," that is, boast (Isa 13:19); for the alliance with it was completed.
isa 20:6isle--that is, coast on the Mediterranean--Philistia, perhaps PhÅnicia (compare Isa 23:2; Isa 11:11; Isa 13:22; Psa 72:10).
we--emphatical; if Egypt, in which we trusted, was overcome, how shall we, a small weak state, escape?
He does not narrate the event, but graphically supposes himself a watchman in Babylon, beholding the events as they pass.