This verse can be confusing because it sounds like the Lord's intentions are to make the people spiritually blind and spiritually deaf. It sounds like the Lord doesn't really want the people to 'be converted and be healed.' Yet, we know that the Lord wants everyone to repent. Therefore, we must understand that Isaiah's eloquent language takes some poetic license. The language used describes not the intent of Isaiah's teachings but their effect upon the people.
What is the effect of prophetic teachings upon the righteous? They are enlightened, seeing spiritual truths never before seen, understanding concepts never before appreciated. What is the natural effect of prophetic teachings upon the wicked? They are outraged; they rebel against the word of the Lord, thereby extinguishing any flicker of light that existed in the deepest recesses of their spirits. Isaiah's teachings would have just such an extinguishing effect upon the people, effectively shutting their eyes, closing their ears, and hardening their hearts.