Answer:
From Luke 1:1-4
1Many have undertaken to draw up an account of the things that have been fulfilled[a] among us, 2just as they were handed down to us by those who from the first were eyewitnesses and servants of the word. 3Therefore, since I myself have carefully investigated everything from the beginning, it seemed good also to me to write an orderly account for you, most excellent Theophilus, 4so that you may know the certainty of the things you have been taught.
From this it is clear that Luke claims to have carefully investigated the accounts of the apostles and others, and that he wants to write an organized record of Christ's life (perhaps he is saying that his account will be organized better than the others?0 so that Theophilus is assured that these things happened.