Michael Card says it well: Luke is the gospel of amazement. The eyewitnesses Luke interviewed, even after 30 years after Jesus, were still amazed by what they had experienced. Of the five or six words for amazement, Luke is the only gospel writer who uses them all.
Meanwhile, Luke’s story is the story of a world turned upside down. It’s the story of radical reversal. Those who should “get it” (e.g., Zechariah) don’t, while those who shouldn’t (e.g., Mary), do.
But you may be skeptical about the whole thing—some guy writing the story of Jesus that he was told by others 30 years after the guy was around. Here’s how I see it: Guitar Player magazine (2012) published a series of articles 
honoring Jimi Hendrix on what would have been his 70th birthday. (He was born on Nov. 27, 1942.) Here, 42 years after his death (on September 18, 1970), they have gathered, from those who knew him, remembrances and commentary to honor the man.
What strikes me is this: this honorarium to Jimi, 40 years after his death, is greeted with applause and wonder, that we finally have written down from those who knew him these wonderful details of his life and person. For some reason my mind goes to Jesus: 40 years after his death several friends wrote down accounts of his life and person, and they are treated with skepticism and contempt, because the 40-year gap makes the stories unreliable and blown out of proportion. Why are we so accepting of the stories of one hero, and so despising of the stories of another?
Also, as in both stories, we are still close enough to the time that there are plenty of people still alive and around who were there, and who knew him, so that the stories can be acknowledged or discredited. This gives the stories credibility, because there are still enough eye-witnesses to verify the accounts.
Luke says in vv. 1-2: “Many have undertaken to draw up an account of the things that have been fulfilled among us, just as they were handed down to us by those who from the first were eyewitnesses and servants of the word.” It’s the same as the Jimi Hendrix magazine issue: the people who knew him and respected him are glad to be asked to tell the story. As Luke says, he wasn’t talking to casual acquaintances, but to people who knew him well. These stories are meant to be a reliable accounting of what really happened and what was actually said.
“With this in mind, since I myself have carefully investigated everything from the beginning, I too decided to write an orderly account for you, most excellent Theophilus, so that you may know the certainty of the things you have been taught.” This is no blind faith or a legendary story, but the science of careful research, the journalism of an orderly account, and the honesty of his trustworthy report.
Feel free to comment and let me know what you think