With this in mind, since I myself have carefully investigated everything from the beginning, I too decided to write an orderly account for you, most excellent Theophilus, so that you may know the certainty of the things you have been taught. - Luke 1:3-4
This is the beginning of the book of Luke, the account of the life of Jesus the Messiah. Luke starts his narrative by saying that many people before him have described the life of Jesus but he would not just take their words as enough, his thirst for the Lord was so big he had to dig up everything for himself, he had to interview the key witnesses to all the major happenings in the life of the Christ.
In this small fragment of the text we see that Luke himself did all the work and when we look back in the history of the church we learn that he did interview Jesus' mother, Mary, and the apostles who were still alive at the time (because some had already been killed in persecution because of Jesus), and many other people whom had been cured or whom had evil spirits expelled from.
But the main part of this text is the focus he had, the main goal when he wrote his account, that is so that Theophilus, and the church, had a comprehensive, in detail, account of the truth behind that person who came down to earth, born from the virgin Mary after being conceived by the Holy Spirit, the person that claimed to be (and indeed He was) God, who performed many miracles, saved many lives through cures or 'exorcisms', communed with the outcasts from society, taught how to live our lives in a way to please God, and finally gave his own life so that we could be saved, we could be forgiven and accepted by our Father; his death, his separation in our place.
Luke's job was thorough, he went far beyond what everyone else did, on the contrary he would have felt it was enough what the ones before him had done, which he didn't. This is something that is not random. Luke's job as a physician, describing the excruciating pain Jesus suffered, as a journalist conducting so many interviews, and as a historian, setting everything up in their correct context, meticulously, serves to emphasize that the history he was about to tell was the truth, the whole truth and nothing but the truth (so helped him God).
By looking at the gospel of Luke we can know for sure, without a doubt, that it is the truth, that Jesus, the son of God, offered himself in our places as a ransom, as a testimony of God's love for us, and is today sitting at the right hand of God just waiting for us, waiting for the day He will come back to take us, his children, to the place we belong by his merit, that is united with our Father in Heaven. God bless.