Not every essay does all three in the first paragraph, and the degree to which an essay declares its structure or methodology may vary widely, depending on how necessary that information will be to the readers. Sometimes, the entire first paragraph will serve no other purpose than to generate interest in the subject or raise a question, leaving the other tasks for the second paragraph. However, this kind of opening requires a lot of skill, and you can lose your readers in the second and third paragraphs if do not make your purpose clear.