The book starts with the phrase “The beginning of the gospel of Jesus Christ, the Son of God.” It’s purpose, therefore, was to present an account of the good news about Jesus.
This gospel takes a more action-packed, no-nonsense approach to the facts, which are probably not in chronological order. While the gospel does not state the identity of its writer, it has only been associated with the Mark of the New Testament. John Mark is mentioned 10 times in the New Testament: Acts 12:12; 12:25; 13:5,13; 15:37-39; Col 4:10; Philemon 24; 2 Tim 4:11; 1 Peter 5:13. Peter calls Mark “my son” [in the faith, figuratively speaking] and places them both together in Rome (1 Pet 5:13).
Papias, the bishop of Hierapolis in Asia Minor, in about A.D. 130 wrote that Mark was a follower of Peter who recorded the stories about Jesus that Peter used in preaching. Shortly thereafter, about A.D. 150, Justin Martyr said the gospel was “the memoirs of Peter.” Since Mark was a very minor character in the New Testament, the attribution of the book to him is most likely true. Later spurious gospels used the names of the famous apostles, for example, the supposed “Gospel of Peter.” (http://carm.org/does-the-gospel-of-peter-belong-in-the-new-testament). Also, the conflict between Paul and Barnabas over John Mark’s abandonment of their mission trip (Acts 15:36-40) would make it unlikely that he would be selected as the author in later tradition, unless it was actually true. Peter, as a gruff fisherman, probably needed all the help he could get to record his recollections of these important events.
The gospel probably dates from the early A.D. 60s, before Peter’s martyrdom in Rome. Even more critical scholars place its writing not later than A.D. 69 because the gospel shows no awareness of the destruction of the Temple in Jerusalem in A.D. 70.
Mark is quite open about the negative information about those around Jesus. The disciples fail to understand Jesus’ message on several occasions (4:13; 6:51; 8:17, 21: 9:10,32). Jesus’ relatives think he is crazy (3:21). Due to the unbelief of those in Nazareth, Jesus cannot do miracles there (6:5-6). Jesus displays many passionate emotions including love, compassion, severity, anger, sorrow, and tenderness. The inclusion of such information bolsters the credibility of the book.