Why did Matthew, Mark, Luke, and John all decide to write on the same events?

(Shouldn't one Gospel account have been enough?)

First off, the books of Matthew, Mark, and Luke are referred to as the synoptic Gospels (excluding the book of John) because they have similar content, fashion, and specific language. They contain many similar records of events that happened during Jesus’ earthly walk. This parallelism is not found in the book of John, who used a different verbiage and style of writing, with a much deeper focus on doctrine regarding the divinity of Jesus and salvation through faith in him.

Interestingly, however, all four Gospels record at least 18 events in common, 14 of which happened during the last week of Jesus’ life.

Moving on, these Gospels were written to preserve eyewitnesses’ testimonies of Jesus’ life for the sake of authenticity and verity across different generations. This proved to be necessary as just decades later, false Gospels began to emerge. Thus, the agreement of different valid records helped even further.

The four gospels—Matthew, Mark, Luke, and John—are the only authentic and authoritative narrations of Jesus’ life; they have apostolic authority, i.e., their knowledge was received in the first century A.D. through eyewitnesses of Jesus’ ministry (basically the apostles) or close associates of the eyewitnesses. Essential beliefs about Jesus, as well as standards for what types of texts were authoritative for Christians, were established during the lifetime of the apostles.

Luke 1:1-4(KJV)

[1]Forasmuch as many have taken in hand to set forth in order a declaration of those things which are most surely believed among us,

[2]Even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word;

[3]It seemed good to me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus,

[4]That thou mightest know the certainty of those things, wherein thou hast been instructed.

Now these four gospels are not identical in outline or detail. Also, although they were written for basically the same purpose, their direct intended audiences (decoders) were not essentially the same.

THE GOSPEL ACCORDING TO MATTHEW has a heavily Jewish perspective; he wrote to persuade Jewish people that Jesus was the true Messiah they were expecting. He did so by connecting Jesus wherever possible with Jewish tradition. For example, he traced the genealogy of Jesus from Abraham (not Adam), quoted often from the Old Testament, exposed the inadequate religious practices of the Jewish leaders, demonstrated Jesus’ power in miracles, emphasized Jesus’ teaching about the true nature of God's kingdom and corrected false ideas centred on an earthly kingdom, while making it clear that the gospel is not for Jews alone but for all nations (28:18–20).

THE GOSPEL ACCORDING TO MARK appears to be aimed at Roman readers; though second in order, it was first in writing. John Mark’s information about Jesus came largely from the apostle Peter. (Mark was not one of the twelve disciples.) This book appears to be addressed to Romans who would wonder why Christians would do such a seemingly foolish thing as to follow a man who had been executed as a common criminal. But describing Jesus’ deeds and teachings, Mark showed how Jesus offended the religious leaders, how they in turn secured his crucifixion from Pilate, and how God overruled that opposition by raising him from the dead. This Gospel shows Jesus as the Son of God, worthy to be believed and followed.

THE GOSPEL ACCORDING TO LUKE was dedicated to Theophilus (1:3) and presumably to readers of Greek background, to convince them of the truth of the things they had heard about Jesus (1:4). Luke tailored his account of Jesus’ ministry to persons without a Jewish background, showing the universal appeal for the gospel. For example, he described Jesus’ birth in the setting of world history (2:1–7), he traced the genealogy of Jesus to Adam (not only to Abraham), he explained unfamiliar Jewish customs, and all in all, he emphasized Jesus’ compassion for all, also showing that Jesus is for the Gentiles too (all nations).

THE GOSPEL ACCORDING TO JOHN was written by John the apostle to convince readers (of whatever background) that Jesus is the Messiah, the Son of God (20:31). Beginning with a fascinating insight which affirms that the same Word by which God created the world in the beginning became flesh in the person of Jesus (1:1–3, 14), John repeatedly mentioned how certain persons and events testify to Jesus. “The disciple whom Jesus loved” (21:20, 24) wrote this book—in a time when Gnostic philosophy was rife—to persuade everyone possible that life is found only in Jesus, through faith in him.

“Matthew composed his Gospel among the Hebrews in their language, while Peter and Paul were preaching the Gospel in Rome and building up the church there. After their deaths, Mark—Peter’s follower and interpreter—handed down to us Peter’s proclamation in written form. Luke, the companion of Paul, wrote in a book the gospel proclaimed by Paul. Finally, John—the Lord’s own follower, the one who leaned against his very chest—composed the Gospel while living in Ephesus, in Asia.”

—POLYCARP OF SMYRNA, a student of John and later a pastor (born A.D. 69)

Every known manuscript of the gospel according to Matthew is written in Greek. Yet Polycarp (and Papias of Hierapolis) report that Matthew wrote his Gospel first and that he wrote in Hebrew. As a result, many scholars believe the apostle Matthew originally wrote Jesus’ teachings in Aramaic, a language that’s closely related to Hebrew. Later, someone—perhaps Matthew or someone associated with Matthew—merged these teachings with portions of Mark’s Gospel to form the Gospel according to Matthew as we know it, in Greek language. Such practices were not unheard of in the first century: Flavius Josephus wrote two histories of the Jewish-Roman War, one in Aramaic and the other in Greek (Conspiracies and the Cross by Timothy Paul Jones, p. 25).

Relevant references:

ZONDERVAN KJV Reference Bible (prefaces)

Timothy Paul Jones’ Conspiracies and the Cross