Mortimer Adler's classic How to Read a Book addresses both the why and how. I'd suggest ... reading it, synoptically, to answer your question.

https://www.worldcat.org/title/how-to-read-a-book/oclc/11137...

Simply: reading is communication over time. It enables earlier others to share their thoughts and insights. Often, as suggested in this thread, ideas arising in one domain have relevance in others --- they provide insights, clarity, metaphors, understanding, mechanisms, skills, ...

Why do you read Hacker News?