Isaiah here speaks of the coming kingdom in which the present kingdom of God will be sanctified. But before kingdoms change, men must change. So also even now to see the kingdom of God one must be born again as Jesus said, "I tell you the truth, no one can see the kingdom of God unless he is born again." John 3:3 There are those who are blind and deaf who don't think they are blind and deaf. Their perceptions are corrupted by sin. But they are not innocent victims. For they willfully shut their eyes and refuse to listen. But the kingdom of God will be characterized by those who sincerely deal with the truth. They listen and don't shy away from the truth. Their perceptions have been sanctified.
And so also they will be sanctified with respect to how they process ideas. Their heart, mind and conscience will be sanctified so that they will understand and know God.
And so also how they express ideas will be sanctified. They will speak the truth with clarity of conviction as one instructs others.
And contrary to the relativism of this post-modernistic society, he will not only hold to truth, but also despise those who don't. The Psalmist speaks also of these characteristics saying in Ps 15:
LORD, who may dwell in your sanctuary? Who may live on your holy hill? He whose walk is blameless and who does what is righteous, who speaks the truth from his heart and has no slander on his tongue, who does his neighbor no wrong and casts no slur on his fellowman, who despises a vile man but honors those who fear the LORD, who keeps his oath even when it hurts.