The Four gospels, Matthew Mark, Luke, and John are quite similar as the all follow the same life of Jesus. Why not just one authoritative gospel? God has his reasons, but I say we are blessed.
Matthew portrays Jesus as a master teacher and lays out 5 great speeches of Jesus. How precious is the complete Sermon on the Mount with the Beatitudes?
Mark presents Jesus as a man of action. How much insight do we get from Jesus family coming to take him away as thought he was crazy?
Luke shows Jesus praising the gentiles and caring for the uncared for. Only Luke draws out Mary. How often do we turn to the stories of the Prodigal Son or of the Good Samaritan? Note the Samaritan is a gentile.
Lets take a different take.
4 Gospels – More Complete
Matthew comes across as ISTJ or INTJ and remembering the old testament and the far distant future.
Mark recounts what Peter said. Peter is very ESTP as is his book of action.
Luke seems ISFJ in his eye on caring.
John is INFP and a dreamer.
These very different personalities give different people a place to latch on to. Matthew can be too boring and John can be too dreamy (in the beginning was the word) Luke can be too soft and Peter/Mark can be sharp.
In the set of four gospels, we get a better picture of the whole from their quite different personalities and quite different focus. God is so clear in what he wants to do and brings out these very different men to recount the life of Christ.