The third Gospel is the only one written by a gentile.  Luke also wrote the book of Acts.  His two works comprise 25% of the New Testament.

Luke was a doctor.  The flavor of the man always comes out in his writings.  In Luke we see more conversation about women, gentiles, and the social outcasts. When a beggar lays at the gate of the rich man, Luke says he was full of sores.  Matthew would have said he was broke.  Matthew’s perspective as a tax collector was his financial status, while Luke had the perspective of a doctor.

Luke’s gospel is written to the Greek, or Gentile world.  He uses Mark as his time line and repeats somewhere around 50% (320 of 661 verses), of the same material Mark provides.

Because he is writing to the Gentile world he begins his genealogy at Adam.  Matthew goes back to Abraham, Mark bypasses the genealogy, and Luke goes back to the first man Adam. John, who writes to the church, reaches back to the misty darkness of eternity.

It appears to me that Luke took the time to interview the people of the early church.  He states that his book is from the beginning and that he had perfect understanding of it all.

When you read of Jesus’ birth in Luke’s account, you find some tidbits of information no one else includes.  One example would be the details of Mary’s song and inner thoughts and feelings.

That causes me to think Luke must have sat down with Mary and spent time talking to her.  I can envision him sitting quietly many years later, at the end of her life, recording her words as she softly speaks of those bygone years.  As she wistfully remembers, he dutifully records.

Not only does he provide information about people’s feelings and inner thoughts, he also documents his writings with names, offices and titles of over 50 people.  This gives his work a credibility the other gospel writers do not have to the world of scholars.

One example of his documentation is the introduction of John the Baptist in chapter 3.  Luke places 7 men in the scripture for historical evidence.  He mentions an emperor, a governor, three tetrarchs, and two high priests.  These are the kind of things that give Luke credibility with the world of scholars.  This also gives further credibility by association to the other Gospels who give the same information.  For this alone Luke is invaluable.

Another contribution of his is the writing of parables spoken by Jesus.  He records 18 parables not recorded anywhere else.  We are indebted to him for the famous parable of the good Samaritan, the prodigal son, and many others.

I am going to go out on a limb here and state my opinion for what it is worth.  I know that Luke traveled with Paul.  I am somewhat sure he joined Paul on one of his missionary journeys, because the text of Acts changes from they, to the first person of I and we.  So my thought is that somewhere Luke sat and listened to Paul tell his insight into the life of Jesus.  My best guess would be  this occurred while Paul was being held at Caesarea.

Just like when he started his book by making the journey to see Mary, I can see Luke taking notes at the feet of Paul and then the Holy spirit washing them though the man Luke with his training, his education, and his perspective.  From out of that flowed the gospel of Luke.

The gospel written to the Greeks adopts the Greek idea of the perfect man.  The Greeks created their Gods by deifying man into a God.

Luke very ably and perfectly adopts their premise and presents them with the perfect man, who was indeed God, Jesus Christ the savior of the world.