Luke’s primary purpose is to edify Christians by recounting how God’s plan, coming to fulfillment in Jesus, had continued to unfold in the history of the early church. Perhaps Luke’s most important contribution is precisely this careful linking of the apostolic proclamation of the Word of God with the word that Jesus both taught and fulfilled. The “Word of God” thus binds together Luke’s two volumes, as the salvation that the angel first announced on the night of Jesus’ birth on a Judean hillside (Luke 2:10-12) is brought finally to the capital of the Roman Empire. Luke thus presents “the things that have been fulfilled among us” (Luke 1:1) as a continuation of the salvific history of the Old Testament, showing how this history reaches its culmination in Christ and flows from him through the Spirit-led apostles into a new phase, the church as the eschatological people of God. By doing so, Luke gave to Theophilus, and continues to give to every Christian who reads his two volumes, an assurance that faith is solidly grounded in the acts of God in history and that the message we believe is the same message sent from God.
-D. A. Carson & Douglas J. Moo - An Introduction to the New Testament