Editing is not one single task. Different stages focus on different parts of a manuscript, and the order matters.
Developmental editing looks at the larger story. It may consider structure, pacing, character arcs, plot logic, point of view and whether the manuscript delivers on its central premise.
Line editing works at sentence level. It focuses on clarity, flow, voice, rhythm and the way language communicates meaning. Copyediting checks grammar, consistency, usage, punctuation and factual or continuity details within the agreed scope.
Proofreading is usually the final check after the manuscript has been edited and laid out. It looks for remaining errors in the text and, where relevant, the designed pages.
Not every book needs the same level of editing. The right process depends on the manuscript's condition and the publisher's workflow. Authors should ask what each stage includes, how feedback is delivered and how many rounds are planned.