I need help on starting an essay on the short story Benito Cereno. The task is an unprompted "thoughtful response" that will be about 2-3 paragraphs long. Can you help me with finding an angle to start the essay with and a theme to follow?

Since this is a personal opinion question, I will offer a few suggestions that you can consider.
One way to approach this writing is by trying to understand why Delano is unable to notice what is going on while aboard the San Dominick. There are several clues as to what is really going on, yet Delano overlooks all of them by explaining away his suspicions. You might explore why he does this, and consider if he is willfully ignorant, unobservant, or simply biased.
Another way you might choose to respond to the story is to discuss the issues of slavery and racism. Is this story pro-slavery or anti-slavery? Does it conform to or challenge stereotypical racist attitudes toward black people? What is Melville trying to communicate about rebellion? Is it good, bad, or somewhere in between?
Finally, you might focus on Babo’s character and analyze his personality. Focus on how Babo keeps Cereno within his sights at all times. What does this reveal about Babo’s character? What about the shaving scene in which he nicks Cereno’s neck? What about his stoic refusal to speak during the court appearances? Is Babo a villain or a hero? Does he represent evil, depravity, or something else?
This work has been hotly debated throughout literary scholarship in regards to which angle Melville uses to address the issues of slavery and race. Some even suggest that the issue of slavery is not the focal point of the story. Consider these options, and good luck in writing your response.