You see the full character of Christ through the four different portraits in Matthew, Mark, Luke and John.
The answer is that it is the nearest Gospel to the Old Testament, the most Jewish one that picks up the threads of all that has gone before.....
We now suddenly realise why Matthew is the first in the New Testament, even if it was not the first to be written.
That is his object.
Matthew paints the King of the Jews.
Each of them is painting a different picture - not a contradictory one, but filling it out with a new aspect.
You see the full character of Christ through the four different portraits in Matthew, Mark, Luke and John