Last month, I finished reading through the book of Isaiah (approximately) twenty times (I spent about a year in it).
Isaiah is a challenging book, for a number of reasons.
The first is length: at 66 chapters it takes a long time to get through one time (about two weeks), and you can forget the beginning by the time you get to the end.
Second, the book is mostly prophetic utterances - not a story or narrative, with clear boundaries (people did this, then they did that). This makes it hard to break up into smaller chunks to be processed.
The third challenge is related to the second - because it is prophetic language, it is often hard to grasp, or unclear in meaning or subject.
Nevertheless, there is a clear message which comes through - that of God's judgement on sin and His provision of salvation.
I took several style of notes as I was reading; in one, I wrote a word or two to summarize a chapter. You see: judgment; salvation; judgement and salvation.
This makes sense in context. Israel had disobeyed God for some time, and was about to go into the Babylonian captivity. We also see many strong messianic prophecies (God ultimate plan of salvation)