In Oswalt’s commentary on Isaiah 41 he writes: “This argument will be repeated and intensified several times in the next few chapters as this court case continues” (p. 459).  You have at least two options: (1) preach the repeated themes as you encounter them along the way or (2) preach the theme in one location, adding any material from the “intensified” places.  I choose the latter option as a way of keeping a series moving along in a long book such as Isaiah.  I’ve found it helpful to read through the section and look for the repetition/restatement.  That allows you to scan for material you want to bring into the one sermon on the presented theme.  More than likely, the same theological message (how the section functions for the church) will be presented throughout the repetition.