I believe to think, you must first learn how to doubt. The inability to think (i.e. the inability to examine your own perspective) comes from believing that your current perspective is the absolute truth and dismissing all others.
There are two ways I see this shift to doubt happening.
#1: Exposure to multiple views of the world. Understanding how others see the world and how their society caused them to view things a certain way and without their own consent.
#2: Experiencing a life event that pokes holes in your current reality (ex. leaving a religion, feeling unfulfilled at work), sending you on a journey of questioning everything you’ve been taught so far.
If a reader can be open-minded enough to take new information without immediately dismissing it as bunk or accepting it as absolute truth, then they are well on their way to getting words from a book into their heads as personally-held beliefs or better yet, an interesting tool in their toolbox of useful perspectives.