Every page of the Tanakh, what Christians have dubbed the Old Testament, describes the Messiah. In some way, every man or woman in the Tanakh tells us something new about that Messiah. Every story leads to The Great Event.
Nothing in the New Testament means anything without the resurrection. Either God raised Jesus from the dead, or we followers are deluded.
However, the Gospels have widely different accounts. They disagree on who first saw Jesus, what Jesus said, where they were, and on things like an earthquake and an angel. Matthew deals with the whole event in just twenty verses, Mark with eight verses—though later copies of Mark include verses 9-20—Luke uses fifty-three verses, and John has fifty-six verses.
It is true that each of the four authors had a specific agenda in mind as they sat down to write—or dictate—the arrival of the Good News of the Messiah, the anointed one of God. Also, they each had different sources, people who remembered specific events.
Matthew sat down with his notes, arranged them in a logical order and began to write. Mark sat down with a set of notes which included different events. Scholars are not sure who wrote first, but there is general agreement that Matthew, Mark, and Luke were written within a few years of each other, about thirty years after the resurrection, and John probably another thirty years after that.
The similarity between writing in the First Century and writing today is enormous. As I work on my historical novel, I can Google any question or detail that I confront. I can read hundreds of books on the subject and have them in front of me as needed. I can keep a nearly endless stack of notes on my computer, or even on note cards if I choose. I can print dozens of copies of my writing if I need to until I get just the right one.
Matthew may have had a hand full of note scrapes written on the backs of discarded wineskins ruined papyrus. Otherwise, he relied on his memory of the stories he had heard over the decades since the events. He probably dictated to a scribe who wrote on an expensive leather scroll until he reached the end of the scroll. It may be that Mark included only eight verses because that was all the space left on the scroll.
It is important for the modern writer to use some of the ancient techniques of planning before writing. We need to avoid writing six-hundred-page books by throwing out interesting accounts that do not further the agenda.
Always build to the most important event, and leave enough space to describe it completely.
Read my earlier comments on this theme here.
Be righteous and do good.