Luke 1:16-17 And he will turn many of the children of Israel to the Lord their God, and he will go before him in the spirit and power of Elijah, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just, to make ready for the Lord a people prepared.”
Before there was Jesus, there was John the Baptist. There had to be. If Jesus had come into the world apart from the way being prepared for Him, the mission would have been compromised. The people were not ready for the Messiah, they needed someone to prepare them. John was that someone.
Long before John’s birth, there was a prophesy of the one who would come in the power of Elijah to prepare the hearts of the people to turn back to God (Malachi 4:6). John’s one role was to make the way for the Promised One, and then it was his time to decrease so that the Savior could increase (John 3:30). Because of the prophesies, John’s parents would have understood what the angel’s revelation to them meant. Their son would be the last prophet before the coming of the Christ.
In God’s sovereignty it just so happens that John and Jesus were relatives. The man who would declare Jesus the “Lamb of God who takes away the sin of the world” (John 1:29) was His own kin. The baptizer who would watch as the Father and the Holy Spirit gave testimony about Jesus (Matthew 3:16,17) had affection for Him as family. Before Jesus could come, John had to come and get things ready for Him.