Isaiah 20:3
And the LORD said, Like as my servant Isaiah hath walked naked and barefoot three years for a sign and wonder upon Egypt and upon Ethiopia; And the LORD said, Like as my servant Isaiah hath walked naked and barefoot three years for a sign and wonder upon Egypt and upon Ethiopia;
Isaiah 20:3 belongs to the section of Isaiah in chapters 13-23 that contains prophecies concerning the nations, including Egypt and Ethiopia. Naked in the verse means stripped of the outer garment rather than completely unclothed, so Isaiah removed his outer robe and went barefoot as a visible sign to the people. The verse records that he walked in that condition for three years as a sign and wonder and warning upon Egypt and upon Ethiopia.
The sign was fulfilled when Sargon, after taking Ashdod around 711 B.C., invaded Egypt and subdued Ethiopia. The actions of Esar-haddon and Ashur-bani-pal also helped bring about a partial fulfillment of the prophecy concerning those nations. The verse gives an example of Isaiah serving as a sign, illustrating how Joshua and his companions were to serve as signs of the Messiah, the Branch. The three-year act was not for Isaiah's comfort or convenience but was a difficult public witness, showing that God's servants may be called to bear an uncomfortable testimony.