A common piece of rhetorical advice is usually phrased this way: “Tell them what you’re going to tell them, then tell them, then tell them what you told them.”
This advice, which some attribute to Aristotle, is great if you’re giving a three-hour speech in the agora. If you’re writing an e-book, magazine article, or blog post…no.
Threefold repetition is ideal for oratory: sermons, lectures, political campaigns. It is not appropriate for most writing, and it’s completely inappropriate for writing on the Internet. Modern readers will quickly lose patience.
A listener needs repetition to aid memory. But if readers have trouble remembering what you wrote, they’ll re-read it.
Long-form writing, especially in academia, often still follows this formula, but it’s really not necessary or helpful.
Modern readers are pressed for time. They want you to get to the point without unnecessary preamble or redundancy.
The White Rabbit put on his spectacles. “Where shall I begin, please your Majesty?” he asked.
“Begin at the beginning,” the King said, very gravely, “and go on till you come to the end: then stop.”
Lewis Carroll, Alice’s Adventures in Wonderland