Speaking frankly, Isaiah flipped! If I go to a friend's home and they have an immaculately clean house; it only makes me that much more painfully aware of the state I left my house in. I believe it was the same for Isaiah. Standing in the face of predation, majesty and glory, he could feel his own iniquities beating down on him. The guilt must have been overwhelming. Instead of destroying Isaiah or some other harsh punishment, which he deserved, God cleansed Isaiah of this sin and removed the guilt. He forgave him. He the asks Isaiah, "Who will go for us." In other words, who will do my work? Who will carry my message? Isaiah accepts.
When I hear a god calling me, a lot of the time I am driven by my flesh to panic just as Isaiah did. I'm not sure if I'm up to the task or good enough. Sometimes I'm called to do things I just don't want to do. Even still. I know that if i am called to it, my Father has already worked it out and I will be successful or taken ca of.