Verse Luke 1: 16-17 " And many of the children of Israel will he convert to the Lord their God.
And he will go before him, in the spirit and power of Elijah the prophet, and will turn the heart of the fathers to the children, and them that are disobedient to the knowledge of the righteous, and will prepare a perfect people for the Lord.
The angel announced 4 things, about he ministry of John the Baptist
1) Will turn children of Israel to the Lord, their God
2) "Will turn the heart of the fathers to the children,. And those who are disobedient will be turned to the knowledge of the righteous". Here the fathers are the prophets, patriarchs and forefathers of Israel. The sons are the fallen children of Israel. John's ministry will turn these fallen children to be like their forefathers who obeyed Lord. And so these fathers will look to the children with affection.
3) Prepare a perfect people for the Lord.
4) The pattern for his ministry would be like the great prophet Elijah (in the spirit and power of Elijah). Jesus later said this was fulfilled in John Matthew 11:14 and 17:12)