The “hook” is the first sentence of your essay introduction. It should lead the reader into your essay, giving a sense of why it's interesting. To write a good hook, avoid overly broad statements or long, dense sentences. Try to start with something clear, concise and catchy that will spark your reader's curiosity.
In this paragraph, as in the rest of the letter, King is justifying his nonviolent campaign for civil rights to eight white Southern clergyman who question if he is going too far.