Isaiah 20:3 & 4
Then the Lord said, 'Just as my servant Isaiah has gone stripped and barefoot for three years, as a sign and portent against Egypt and Cush, so the king of Assyria will lead away stripped and barefoot the Egyptian captives and Cushite exiles, young and old, with buttocks bared - to Egypt's shame.
We see that Isaiah walked around this way for three years. We are reminded that, throughout the Bible, the number three is associated with the earthly display of God's will. The purpose of Isaiah's walk of faith was to be an example of what would happen to the Egyptians and Cushites at the hands of the Assyrians.