"Mark is known for the understated irony of his gospel, but there is a large-scale irony overarching the book that is worthy of Sophocles. Readers know from the first verse of the gospel that Jesus is Son of God, and that title is used periodically through the gospel by the Father and by demons. But no human beings recognize Jesus as Son until the centurion at the cross. There is the ironic distance between our knowledge and the knowledge of the characters in the story. But that irony is eventually doubled back on the reader: Would we recognize Jesus as Son of God while He’s dying in anguish?" -- Peter Leithart
Also on Mark: Terry Virgo recommends James Edwards Pillar Commentary.I'd agree, it's very helpful - typical of the Pillar series.