We know from the Bible that it would have been morally unacceptable for Isaiah to go about entirely naked (Genesis 9:20–27). To go about completely naked would have been shameful and would have had a negative influence on his prophetic influence. The addition of the word “barefoot” indicates that he was not completely naked, otherwise there would be no need for this description. He would have been dressed in the long tunic that served as underwear.
2 at that time the LORD spoke by Isaiah the son of Amoz, saying, “Go, and loose the sackcloth from your waist and take off your sandals from your feet,” and he did so, walking naked and barefoot.