If Luke has carefully designed his two-volume history, we should probably pause to wonder why he includes such lengthy description of the journey to Rome. This must be more than an exciting story (did he think readers were getting bored?), nor was Luke trying to fill out a scroll (as if he was a student trying to make it to 10 pages for a paper). There are literary and theological reasons for Luke’s inclusion of Paul’s shipwreck.
First, Luke is traveling with Paul. On the one hand, this accounts for the details. But often ancient historians narrate a story up to the time in which they are living and then include themselves in the story in order to build credibility. Josephus summarized all of Jewish history up to the time of the Jewish revolt and included himself in the story as a leader in Galilee. Thucydidies wrote a history of the Peloponesian War and included his own participation at various points. This shipwreck functions to give Luke credibility – he witnessed the events himself and was a participant in the history he tells. A Greco-Roman reader would expect this sort of thing if the book of Acts was to be seen as credible.
Second, there is more going on here than Luke’s interest in travel. If someone (say, Theophilus) has been reading through Luke and Acts, he would notice some similarities between Paul and Jesus. Both are arrested by the Jews and handed over to the Romans, both are tried by a secular authority (Pilate and Herod; Felix/Festus and Agrippa) and both are the victims of a miscarriage of justice motivated by the religious establishment in Jerusalem. Will Paul suffer the same fate as Jesus? Will he be executed by the Romans as a political undesirable, or will he receive justice from Rome?
Third, we need to remember Luke’s theme for the whole book: “beginning in Jerusalem, then Judea and Samaria, then to the ends of the earth.” Luke knows that Paul will go to Rome to testify before the Emperor, but the reader may think that Paul will be killed along the way. As James Dunn has observed, Luke is trying to show that “come what may, God will fulfill his purpose by having Paul preach the good news in the very heart of the empire.”
Fourth, some scholars question the historicity of the shipwreck based on parallels with other ancient literature, including Homer’s Odyssey. Often a guilty man will try to escape justice (or fate), head out to the seas to avoid capture, but ultimately he will suffer and die anyway. Paul is escaping from the Jews, yet is shipwrecked and eventually nearly killed by a snake, it is thought that Luke is patterning this story after the archetypal Greco-Roman novel plot-line.
There is something to the parallels and it may be Luke tells this story in such detail because shipwrecks were popular in literature at the time. But this does not necessarily negate the historicity of the story. Paul went to Rome, the best way to do that is by ship. It is entirely plausible Festus would send him off in this way. Shipwrecks were in fact common, so much so that Paul has already suffered shipwrecks twice in his travels (2 Cor 11:25)!
While I think Paul did travel to Rome by ship and experienced a shipwreck, Luke’s theological motivation is that nothing will hinder the Gospel getting to Rome.