The Gospel of Luke tells the good news of the earthly ministry of Jesus Christ, the son of God. Its sequel, Acts, tells the good news and the acts of the Holy Spirit during the early decades of the Christian church. The two books fit together seamlessly and when combined make up more than 25% of the entire New Testament.
Luke states that the reason he wrote this account, was so that you may know the exact truth about the things you have been taught (v 4).