“If you want to learn something for the long run, you have to write it down. If you want to really understand something, you have to translate it into your own words. Thinking takes place as much on paper as in your own head.” — Sönke Ahrens
Reading is not enough. Highlighting is not enough.
Reading is entertaining. Highlighting is great for quotes and references. Both do little to stimulate the mind.
How much of what you read or highlight is put to good use? How much is even remembered? How many ideas confront you while reading, only to be left behind? Quite a few, I dare say.
Try a little experiment:
Read something of interest.
Write a note about it in your own words.
Make the note concise.
Read it aloud.
Did the words flow effortlessly? Possible... but unlikely. Most people struggle with describing something in their own words. Why is that?
You are trying to understand what you just read. In fact, you MUST understand it to describe the underlying idea in your own words. Making what you write concise requires an even deeper understanding. And that is entirely the point.
Writing a note, especially when concise, forces you to confront how well you understand what you read. It is similar to the concept of teaching. You must understand something to explain it in simple terms to someone else. In this case, that someone else is you.
Writing and understanding are therefore inextricably linked.
Seeing your words in front of you. Reading them aloud. Thinking. Rephrasing what is initially clumsy or unclear. It stirs something deep within you.
Writing even a small note stimulates the mind in ways reading and highlighting alone can never hope to do. It links thinking with understanding and accelerates both.
Writing is the medium of understanding.