The following is taken from the FAQs answered by Don Stewart, available at the BLB.
Each Gospel Was Written For A Distinct Purpose
It is important that we understand these sources and what they are trying to accomplish. The Gospels are neither biographies of the life of Christ nor are they a disinterested record of certain events in His life. Each writer wants the reader to know the truth about Jesus and become a disciple. To accomplish this purpose, each Gospel is aimed at a certain audience and each writer is selective of the events he includes.
Matthew
The Gospel according to Matthew is aimed primarily at the Jew, the person familiar with the Old Testament. Jesus is portrayed as Israel’s Messiah, the King of the Jews. Matthew records how the promises God made in the Old Testament, with regard to the Messiah, are fulfilled in Jesus. Matthew begins his book by stating the family tree of Jesus:
The book of the genealogy of Jesus Christ, the Son of David, the Son of Abraham (Matthew 1:1).
This genealogy demonstrates that Jesus is the rightful heir to the kingdom that was promised to David and his descendants and sets the tone for the book. The remainder of the book emphasizes that Jesus has the credentials to be Israel’s Messiah.
Mark
Mark, on the other hand, is not writing to the Jew or to those who are familiar with the Old Testament. His audience is basically those people in the Roman Empire who are unfamiliar with the religion of the Jews. Consequently, Mark’s Gospel does not start with the birth of Jesus or any family tree that demonstrates Jesus as a fulfillment of prophecy. It starts, rather, with the beginning of Jesus’ ministry.
The beginning of the gospel of Jesus Christ, the Son of God (Mark 1:1).
Mark’s is a Gospel of action. Jesus is portrayed as the servant of the Lord doing that job that God has sent Him to do. Thus, the emphasis is on doing, and Mark shows that Jesus got the job done. Consequently Mark’s gospel records more miracles of Jesus than Matthew, Luke, or John.
Luke
Luke was written to those more intellectually minded. He states his purpose in the book’s prologue:
Inasmuch as many have taken in hand to set in order a narrative of those things which are most surely believed among us, just as those who from the beginning were eyewitnesses and ministers of the word delivered them to us, it seemed good to me also, having had perfect understanding of all things from the very first, to write to you an orderly account (Luke 1:1-3).
Luke is not writing as an eyewitness but as one who is recording eyewitness testimonies. His portrayal of Jesus is as the perfect man. Hence, he focuses on those events in Jesus’ life that stress His humanity. The Greeks in their art and literature were always looking for the perfect man. The Gospel of Luke reveals that man.
John
John, the writer of the fourth gospel, was an eyewitness to the life of Jesus. The things he recorded were for the purpose of establishing the fact that Jesus was the eternal God who became a man. John wanted his readers to exercise faith toward Jesus.
And truly Jesus did many other signs in the presence of his disciples, which are not written in this book; but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in his name (John 20:30,31).
When John states his purpose he also states that he is selective in what he has recorded.
Summing Up The Testimony Of The Four Gospels
We can sum up the testimony of the four gospels in the following manner.
In Matthew, Jesus is the Son of David (Isaiah 11:1; Matthew 1:1)
In Mark, Jesus is the Son of Man (Zechariah 3:8; Mark 8:36)
In Luke, He is the Son of Adam (Zechariah 6:12; Luke 3:38)
In John, Jesus is the Son of God (Isaiah 4:2; 7:14; John 3:16)
Summary
The four gospels were written to cover four aspects of the life and ministry of Jesus. Each gospel writer wrote from a different perspective to a different audience. They each looked at the character of Jesus from different angles. Thus the number of four arises from the four different perspectives we have given about Christ’s life and ministry.
Each author is presenting a different aspect of Jesus’ character. In Matthew Jesus is the king; in Mark; He is the servant; in Luke; He is the perfect man; in John, He is God. This is because each writer addressed a different type of audience.
The Gospels are not intended to be a history or biography of the life of Christ in the modern sense of the term. Each author is selective in what he portrays. Jesus did many more things than the Gospels record as John testified.
When the Gospels are compared with each other we get an overall portrait of Jesus. He was God from all eternity who came down to earth as the perfect man. He was the Messiah of Israel, the King of the Jews, the one who did the job that God sent Him to do. This is the testimony of the four Gospels.