reading as a process
Reading (and learning in general) is a process, not a product. It is not something that you can own or collect. Once a book is finished, you do not have the contents in your brain. You must make connections with other knowledge. These connections are the truly important part of reading.
References
This came from listening to the Ezra Klein Show episode This Is Your Brain on ‘Deep Reading.’ It’s Pretty Magnificent from Nov 22, 2022.