Luke writes to Theophilus about the things done among the disciples of Jesus.
God sent a son, John, to Zechariah and Elizabeth, to fulfill the prophecy in Malachi 4: he would be the one in the spirit of Elijah, turning fathers hearts to their children. The same Gabriel that explained the 70 7's to Daniel at the beginning of them, now comes to Zechariah at their end. But he encounters unbelief, in the old man, a stark contrast with Abraham, who also received news from angels that he would have a son in his old age.
Gabriel continues referring to his Old Testament ministry when he goes to Mary, mentioning the everlasting kingdom of Daniel, to be fulfilled in Jesus. Mary asks the same question Zechariah did, but in faith. She sings in the Spirit, rejoicing in God for saving Israel, keeping His promises to Abraham.
Meanwhile, John is circumcised and Zechariah calls him John, at which God opens his mouth. He then praises God in the Spirit for sending a savior, as He promised by covenant with Abraham that He would.
The divine Word with God at the beginning, who made all things, gives light to all men. He came into the world, with John testifying to Him, ahead of Him. But the world He made didn't receive Him. Those who did, He made children of God, supernaturally born again. This Word became flesh, a real man, living among us, His glory seen among us.