Why are there four Gospels and why the synoptic gospels? If there were only one record, with no repetition, critics would say the single record was edited and updated. Since there are four, the critics claim, due to repetition, they are copied.
The problem with this kind of speculation is that it reduces inspiration to a human level and attributes to an unknown editor or editors what the Bible attributes to the Holy Spirit.
The value of repetition is that it gives emphasis to certain themes and provides more witness to an event God has established that a thing should be verified by two or three witnesses, Deut. 19:15, Matthew 18:16. He has given us these witnesses, each inspired by the Holy Spirit. There are differences in some accounts but never any contradictions. Seeing Christ through threefold synoptic Gospels provides a three-dimensional picture of our Lord.
Imagine three witnesses at a trial that say exactly the same thing. The conclusion would be that they have corroborated and their story is rehearsed. Now imagine three witnesses that say the same thing, each with added detail and in different words. The latter is creditable, the former would not be. This is a picture of the synoptic Gospels. Matthew seems to focus on an event with the Old Testament in mind, Mark on the present, and Luke on the future. Matthew puts emphasis on the kingship of Christ, Mark on His life as a servant, and Luke on the manhood of Jesus.
Matthew seems to address the Jews, Mark the Romans, and Luke the Greeks. The main theme of Matthew is His royalty, Mark on His power, and Luke on his Love. Matthew accentuates Jesus’ prophetic position, Mark on practical matters, and Luke on historical things. In reading John (not a synoptic) we find collateral information addressing eternal matters, the gentile church, spiritual issues, and Christ as the Son of God with evidences that prove it.