Most textbooks are very large and contain a great deal of information.
This is partly to be complete but also because it is easier to sell a large book at 40 than a small one at 5. Some of the more modern books will help. Their text is broken into small paragraphs and at the head of each paragraph is a key sentence stating the essential information in that paragraph. Sometimes it is in a different colour, i.e. red print. This will reduce the amount of information that you have to remember.