It had been 400 years since the last prophet had been on the scene, who gave this word of hope to the nation of Israel:

“Behold, I am going to send you Elijah the prophet before the coming of the great and terrible day of the Lord . He will turn the hearts of the fathers to their children, and the hearts of the children to their fathers [a reconciliation produced by repentance], so that I will not come and strike the land with a curse [of complete destruction].”
Malachi 4:5‭-‬6 AMP

John the Baptist’s birth was prophesied before the coming of the Messiah. He would preach repentance with Holy Spirit power, a voice calling in the wilderness (Isaiah 40:2-3), to prepare the way for Him.

Small wonder, then, that his birth was announced by an angel to a couple whose whole lives were dedicated to God. Zechariah and Elizabeth were both from priestly families.

John was the herald who would announce the coming of Messiah to the world!