Should i be mastering every chapter as i go?


Hey everyone, enjoying the book so far but have a general question. I feel i have been getting a good grasp of everything up to chapter 19. At that point i slowed down and thoroughly sorted out chapter 19 to fully understand it. Since then i feel like new classes are thrown out at rapid speed without really much explanation of the pre-built methods and such. Should i be fully memorizing these as i go or be reading these chapters and knowing its a good reference? Example of this is when i am reading the call-back chapter. There is SO much information here i feel, so many classes, methods, that arent really elaborated on, but shown. How should i be approaching the later half of this book?