Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
The Prophet Isaiah a sign to Egypt and Cush or Ethiopia, that the captives and exiles of these countries shall be indignantly treated by the king of Assyria, Isa 20:1-6.
Tartan besieged Ashdod or Azotus, which probably belonged at this time to Hezekiah's dominions; see Kg2 18:8. The people expected to be relieved by the Cushites of Arabia and by the Egyptians. Isaiah was ordered to go uncovered, that is, without his upper garment, the rough mantle commonly worn by the prophets, (see Zac 13:4), probably three days to show that within three years the town should be taken, after the defeat of the Cushites and Egyptians by the king of Assyria, which event should make their case desperate, and induce them to surrender. Azotus was a strong place; it afterwards held out twenty-nine years against Psammitichus, king of Egypt, Herod. 2:157. Tartan was one of Sennacherib's generals, Kg2 18:17, and Tirhakah, king of the Cushites, was in alliance with the king of Egypt against Sennacherib. These circumstances make it probable that by Sargon is meant Sennacherib. It might be one of the seven names by which Jerome, on this place, says he was called. He is called Sacherdonus and Sacherdan in the book of Tobit. The taking of Azotus must have happened before Sennacherib's attempt on Jerusalem; when he boasted of his late conquests, Isa 37:25. And the warning of the prophet had a principal respect to the Jews also, who were too much inclined to depend upon the assistance of Egypt. As to the rest history and chronology affording us no light, it may be impossible to clear either this or any other hypothesis, which takes Sargon to be Shalmaneser or Asarhaddon, etc., from all difficulties. - L. Kimchi says, this happened in the fourteenth year of Hezekiah.
Walking naked and barefoot - It is not probable that the prophet walked uncovered and barefoot for three years; his appearing in that manner was a sign that within three years the Egyptians and Cushites should be in the same condition, being conquered and made captives by the king of Assyria. The time was denoted as well as the event; but his appearing in that manner for three whole years could give no premonition of the time at all. It is probable, therefore, that the prophet was ordered to walk so for three days to denote the accomplishment of the event in three years; a day for a year, according to the prophetical rule, Num 14:34; Eze 4:6. The words שלש ימים shalosh yamim, three days, may possibly have been lost out of the text, at the end of the second verse, after יחף yacheph, barefoot; or after the same word in the third verse, where, in the Alexandrine and Vatican copies of the Septuagint, and in MSS. Pachom. and 1. D. 2 the words τρια ετη, three years, are twice expressed. Perhaps, instead of שלש ימים shalosh yamim, three days, the Greek translator might read שלש שנים shalosh shanim, three years, by his own mistake, or by that of his copy, after יחף yacheph in the third verse, for which stands the first τρια ετη, three years, in the Alexandrine and Vatican Septuagint, and in the two MSS. above mentioned. It is most likely that Isaiah's walking naked and barefoot was done in a vision; as was probably that of the Prophet Hosea taking a wife of whoredoms. None of these things can well be taken literally.
From thy foot - רגליך ragleycha, thy feet, is the reading of thirty-four of Kennicott's and De Rossi's MSS., four ancient editions, with the Septuagint, Syriac, Vulgate, and Arabic.