David observes that it is the fool who lives as if there is no God, and yet he also observes that 100% of us live that way. Yet, there is a group of people God calls "his own," a group he calls "righteous." So the question becomes, who are those people, why has God chosen them, and how do you move from "all have sinned" to "and are justified freely"?
As Paul and Barnabas travel to Antioch, they are invited to speak at a synagogue. Paul launches into his first recorded sermon, and proclaims that God’s promises to Abraham and David are fulfilled in Jesus Christ! The blessing to Abraham in Genesis 12 pointed to Jesus, forgiving our sins and justifying us through his death & resurrection.
Luke starts out his second narrative like a new driver adjusting the rearview mirror, remembering where we've come from in terms of Jesus' life, death, resurrection, and ascension. He reminds us of the promise of the Father, and gets us ready for the mission: Be My Witnesses. And then he ascends.