Isaiah could be thought of as two main sections with a center story. The story is of the salvation of Jerusalem from captivity, covered in Chapters 36-39, and the two sections are on either side.
There is a commissioning of Isaiah as prophet in both sections. The first is in Chapter 6 (most likely placed there chiastically in the first part, which covers chapters 1-12). The second is in Chapter 40.
In Chapter 6, Isaiah is called to a ministry that will not be heard. In Chapter 40, he is called to a ministry of hope that must be heard.
In Chapter 6, Isaiah is called to judge the people. In Chapter 40, he is called to comfort the people.
Judgment and salvation. Exile and return. Demolition and reconstruction. Death and resurrection.