Luke says many accounts were already in circulation, based on reports from eyewitnesses and ministers of the word. He writes after careful investigation to provide an orderly account for Theophilus. His stated purpose is that Theophilus may know the certainty of what he has been taught (Luke 1:1–4).
In Luke 1:1–4 the writer explains why he is writing and how he plans to do it. He notes that many others have already attempted to write narratives about events “fulfilled among us.” Those accounts ultimately trace back to people who were present from the start and who served as public messengers of the message. These lines function as the book’s opening explanation of method and aim before any story begins. The writer positions his work alongside other existing narratives, while also stressing a connection to early eyewitnesses and recognized transmitters of the message.
Luke begins by saying his book is not the first attempt to tell the story. “Many” had already written accounts about events the community understood as having reached their intended outcome (“fulfilled among us”). That framing presents the Jesus story as public, shared history for a community, not just private ideas.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Luke 1:1-4, then read the surrounding section so the answer stays connected to the passage's flow.
1Because many have undertaken to draw up a narrative concerning those matters which have been fulfilled among us,
2even as they delivered them to us, who from the beginning were eyewitnesses and ministers of the word,
3it seemed good to me also, having traced the course of all things accurately from the first, to write to you in order, most excellent Theophilus;
4that you might know the certainty concerning the things in which you were instructed.