Origen
Catena Aurea · Lukasevangelium 1
Forasmuch as many have taken in hand to set forth in order a declaration of those things which are most surely believed among us, Even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word: It seemed good to me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus, That thou mightest know the certainty of those things, wherein thou hast been instructed.
St. Luke hereby explains to us the source of his writing; seeing that what things he wrote, he gained not from report, but had himself traced them up from the beginning. Hence it follows, It seemed good to me also, having carefully investigated every thing from the very first, to write to thee in order, most excellent Theophilus.