Jamieson, Fausset and Brown on Isaiah 20:2

2. by--literally, "by the hand of" (compare Eze 3:14).

sackcloth--the loose outer garment of coarse dark hair-cloth worn by mourners (2Sa 3:31) and by prophets, fastened at the waist by a girdle (Mt 3:4; 2Ki 1:8; Zec 13:4).

naked--rather, "uncovered"; he merely put off the outer sackcloth, retaining still the tunic or inner vest (1Sa 19:24; Am 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.