Luke 1:2

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

The eyewitnesses and ministers of the word are the apostles who from the beginning personally saw the events of Jesus' life. What was delivered came through those who had directly beheld it, not through distant report. God enabled these same eyewitnesses to write the Gospels. In doing so they accurately recorded what they had seen, the truths Jesus had spoken, and things to come.