Readings contain numerous unfamiliar names and details.
Therefore it is important that you keep asking when you read what are the main themes or main points. You do need to have some command of detail, but generally that which is important is frequently repeated. Reading an item once is probably not enough, partly because you tend not to know what is important until you have been through it the first time. I would recommend first skimming, then going back and reading for more detail. If you let your highlighter do the thinking for you on the first time through, the odds are you have few pages that are not all highlight.