"They won't listen, but tell them anyway."
That's quite often what God seems to say to the prophets. The people are blind and deaf, but I still want you to hold up signs in front of their eyes and shout my message into their ears.
There's a basic paradox going on here - we can't see what God sees. Isaiah was deafened by the din of heaven and blinded by the smoke of incense. He couldn't even see God seated on the throne, yet God can see clearly every little habit-forming choice that every little human being is making every little moment of their little lives.
God knows exactly what they're doing to themselves. They're heading for ruin and desolation, and they don't know and don't care.
They're in a pleasure boat, heading for a waterfall. And Isaiah's just been given the job of ringing the alarm bells.