In Luke 1:1-4 Luke tells us why he is writing the Gospel. He is giving what the eyewitnesses and ministers of the word had delivered. Those are two separate but reinforcing categories. The eyewitnesses to the ministry of Christ saw those events with their own eyes. The ministers of the word is that word which makes God known. We have a description of this in John 1. This is not only the word incarnate but the broad sense of the word. The eternal word, the word as the light of man, the word in creation, the word in scripture, and the word incarnate. And this is meant to give us certainty. We can have certainty about the historical events by knowing other basics things about God and our need for redemption from sin.