The passages in Acts that are written in the first person plural point of view are 16:10-17; 20:5-15; 21:1-18; 27:1-28:16 and support this hypothesis. (Guthrie 116) This narrows down the possible people who took part in the authorship of Luke. There are a few occurrences that further imply that the author was a companion of Luke. "The first incident is that the author first joins Paul at Philippi. Also, a second event that occurs is the author reappears on Paul's return to Philippi. A third incident is that he accompanies the apostle on the journey towards and stays with Philip at Caesarea. A fourth incident happened during Paul's two year imprisonment at Caesarea."(Guthrie 116) The author was with Paul when he was going to Rome and became involved in a shipwreck with him. Furthermore, the visits to Jerusalem in Acts confirm the independence of both accounts and still support the idea of Lucan authorship. .
Not only can the author be assumed as a companion of Paul, he can be considered an evangelist as well. The knowledge in the Old Testament can also give us an insight on the authorship of Luke. It is so detailed that others have contended that he must have come to Christ with a background of being Jewish. "A solution that does justice to both sides of the issues is to posit that the evangelist was a Gentile who had become a proselyte or a God-fearer, i.e., was converted or attracted to Judaism some years before he was evangelized." (Brown 268).
It is significant to understand the type of audience that the Gospel of Luke was directed to and where it was derived from in order to find out more information on the authorship. Although Luke the evangelist was said to have come from Antioch, it doesn't give us any hint as to where the gospel was written. By the tradition of Luke being a companion of Paul, it is likely that Luke was addressed to the churches descended from the Pauline mission.