Give me a sentence to start my paper on Why would I like to become apart of this organization

Try telling them you have an overwhelming need to one day be the CEO of such a company and you can think of no better organisation in which to dedicate yourself to learning the crafts you will need and whether you succeed or not your employers are bound to benefit from your enthusiasm.

I would suggest thinking about the why, how , what .
https://student.unsw.edu.au/essay-writing-basics
What parts of the organisation ( research it ) attract you
How do you see yourself fitting in to the organisation and where.
Why do want to be a part of the organisation
What do you have to offer that fits in with the organisation
Research the Mission statement and Organisational Strategy of the organisation in question.
Research opportunities for new employees in the organisation
Once you have the logical break down you can start with a brief statement on why, how and what and then further elaborate on what each logical part has and conclude with how it all fits in with you and the organisation.

Research Research Research !!
Research how to write an essay at University level.
Google it or go to the university library or your University student services in your university may hold courses also on how to write essays or have books available.