what is the authors purpose in writing othello?

http://www.sparknotes.com/shakespeare/othello/

Look particularly at the Context section - 4th paragraph.
Then look at the section on Themes and Motifs. I think you will find what you are looking for there.

To understand the author's purpose in writing Othello, we can look at several factors:

1. Historical Context: Othello was written by William Shakespeare around 1603, during the Elizabethan era. At the time, England was experiencing increasing contact with other cultures and colonizing different parts of the world. Shakespeare might have wanted to explore themes of racial prejudice, cultural clashes, and the challenges faced by individuals in multicultural societies.

2. Entertainment: Shakespeare was primarily a playwright, and one of the main purposes of writing Othello, like his other plays, was to entertain audiences. The play contains elements of tragedy, romance, and suspense, which were popular among theater-goers during that time.

3. Moral and Social Commentary: Shakespeare often used his plays to comment on the human condition and explore complex moral dilemmas. Othello addresses themes such as jealousy, betrayal, trust, love, and the destructive consequences of unchecked emotions. It delves into the flaws of human nature and exposes the tragic consequences of irrational actions.

4. Character Study: Othello is a character-driven play, and Shakespeare's purpose may have been to delve into the psychology and motivations of his characters. The dynamics between Othello, Iago, Desdemona, and other characters raise questions about trust, manipulation, and the nature of evil.

Overall, the purpose of Shakespeare in writing Othello extends beyond a single meaning or motivation. It combines entertainment, social commentary, moral exploration, and character study to create a complex and thought-provoking play.