Mark appears to be written for an audience in Rome. A Roman centurion’s declaration near the end of the book—Surely this man was the Son of God!—models the witness to Jesus this gospel calls for.
The opening half of this fast-moving drama keys on the question: Who do you say I am? An episode at the end of the first half shows Jesus healing a blind man in two stages, so that he slowly comes to see. In the same way the disciples have only gradually come to recognize who Jesus is. Then in a key moment in the story, between its two halves, Peter confesses that Jesus is the Messiah.