Acts 1:1

St. Luke, who was the author of this history, alludes, in this verse, to his gospel, which he calls his first discourse. In that he informs us, not only of the actions, but also the doctrines of our Saviour. These words, to do and to teach, are the abridgment of the whole gospel: here he gives us the Acts of the Apostles, that is, an history of their travels and preaching. In the beginning of this work he speaks of all the apostles, and what they did before their dispersion. As soon as he comes to the mention of St. Paul, he takes notice of no one else, but is entirely taken up with the narrative of his actions. He addresses his book to Theophilus, which signifies a friend of God, or one who loves God, as if he intended to dedicate it to all the faithful, who believed in, and loved God. But it is more probable that this was the same distinct person, well known to St. Luke, and illustrious for his birth, because he gave him the title of Greek: kratiste, most excellent. [Luke i. 3.] (Calmet)