Known Sources
The gospels of Matthew and John were written by eyewitnesses of Jesus' entire ministry. The Lord promised his disciples (which included Peter) that they would remember what they heard and saw so that they could later testify of the truth to the entire world (John 14:26, Acts 1:8).
The gospel writer Luke, however, did not witness the Lord's ministry like Matthew, John or Peter. He was a Gentile (non-Jew) who became a Christian at least a decade after the start of the New Testament church.
The source of Luke's gospel was not his own experiences but rather his diligent research into existing documents discussing Jesus' ministry. He also interviewed, in Jerusalem, many of the twelve apostles and Jesus' mother Mary (Luke 1:1 - 4).
"Luke used the accounts of numerous eyewitnesses to compile his Gospel . . . From the introductions to the Gospel of Luke and the book of Acts, it is apparent that Luke primarily used the written records of the apostles and the original disciples to write his Gospel . . ." (Holy Bible, a Faithful Version, chapter 6).
Additionally, unlike Matthew, John or even Mark, Luke relied on what Paul was personally taught by Jesus (Galatians 1:11 - 12, 16 - 17) for his gospel. Paul also likely supervised what Luke wrote.
A New Testament Mystery
Where did Mark get the information for his gospel? Was it from his own experiences?
Mark, a Jew, lived in Jerusalem with his mother (Mark 12:12). He was roughly around 14 years old when Jesus' ministry began and still a teenager when he fled naked from Gethsemane in 30 A.D. He likely saw at least some events (e.g. the Lord's arrest, Mark 14:51 - 52) that took place in Jerusalem and heard some of the Lord's teachings.
Mark was, however, too young to have traveled with Christ and been an eyewitness, like Peter and others, of his entire ministry. The Bible offers no evidence that he traversed Judea, Samaria and other areas with Jesus and his close disciples.
Mark additionally, unlike Luke, lays no claim to have conducted extensive research or interviewed witnesses for his book. What or who, then, could have been the source of his gospel?
A Special Relationship
Both Peter and Mark lived in Jerusalem from 30 to 42 A.D. It is highly likely that Peter was instrumental in Mark's conversion as he refers to him as "my son" in 1Peter 5:13 (Believer's Study Bible).
Peter felt close enough to Mark and his family to make their house his first destination after he was miraculously freed from prison (Acts 12:1 - 17). Years later the pair were together while the gospel was being preaching in the ancient city of Babylon.
The church in Babylon, chosen together with you, greets you, as does Mark, my son (1Peter 5:13).
Why?
Why would Peter use someone like Mark to write down his account of Jesus' life and ministry? Why not write it himself?
Mark, as a Levite (see Acts 4:36, Colossians 4:10), was perfectly suited to write down Peter's gospel. He came from a wealthy family (his mother owned a huge home in Jerusalem with servants, Acts 12:12 - 13) who could afford to educate him. Peter, on the other hand, was considered uneducated (Acts 4:13).
Mark likely used his talents as a skilled amanuensis (secretary) to help write down Paul's words that became the books of Ephesians, Colossians and Philemon. He also used them to record 1Peter and likely 2Peter as well. His skills were such that Paul, just before his death, requested Timothy bring him to Rome for one final task.
"Knowing he would soon be martyred, Paul urgently began to complete the canonization of his Epistles . . . in order for Paul to complete his work, he needed Timothy - and Mark.
"Paul summoned Timothy, specifically requesting that he bring Mark as well (see 2Timothy 4:11). Mark had previously assisted both Paul and Peter, and would be invaluable in helping Paul edit his Epistles and complete his canonization before his death . . ." (Holy Bible, a Faithful Version, chapter 9).
The Hidden Inspiration
Many Biblical commentaries agree that the Gospel of Mark is, in fact, the Gospel of Peter.
"The early Church believed that St. Mark’s Gospel was in reality the Gospel of St. Peter, and that Mark simply put down the words and memories of his master and friend the Apostle Peter." (Popular Commentary on the New Testament).
"The ancient testimony of Papias, in the early second century, that Mark was the secretary of the apostle Peter (and not the actual eyewitness himself) has such good credentials, and the internal evidence of the Gospel itself is so compatible to this view that it seems evident that the Gospel of Mark is really the Gospel of Peter" (Restoring the Original Bible, pgs. 335 - 336).
"It is the current and apparently well-founded tradition that Mark derived his information mainly from the discourses of Peter." (Illustrated Bible Dictionary).
"A second point is equally clear - that the gospel of Mark is substantially Peter's." (International Standard Bible Encyclopedia).
Capturing His Personality
The marks of Peter's sometimes hyperactive and impulsive personality, not unlike someone with ADHD, are clear in Mark's gospel. He seems to have captured not only the testimony of Peter but also his somewhat restless, hyper nature.
"The account in Mark shows the characteristic haste of Peter in the way it rushes on from one story to the next" (AMG Concise Bible Dictionary).
"In Mark we have no attempt to draw up a continuous narrative. His Gospel is a rapid succession of vivid pictures loosely strung together without much attempt to bind them into a whole . . ." (Illustrated Bible Dictionary).
Mark's experiences or any research he did were not the primary basis for his gospel. He, instead, relied on the hidden source of Peter's memory which Jesus promised would bring into his remembrance everything he saw and heard (John 14:26).