Why is a raison like writing desk?

It seems you might be asking about the word "raison d'être," which is French for "reason for being." It's not related to a writing desk in any way.

"Raison d'être" is a philosophical term used to describe the fundamental purpose or reason for something's existence.

For example,

* The raison d'être of a business is to make profit.

* The raison d'être of a school is to educate students.

Let me know if you were asking about something else!