Why does Elijah turn the hearts of fathers and children to each other?
Malachi 4:6 states Elijah turns the hearts of fathers to children and children to fathers so that God does not smite the earth with a curse. This occurs before the great and dreadful day of the Lord, when God sends Elijah the prophet.
Les teaches from Malachi 4:5 that God will send Elijah the prophet before the coming of the great and dreadful day of the Lord. Verse 6 gives the purpose: Elijah shall turn the heart of the fathers to the children and the heart of the children to their fathers, lest I come and smite the earth with a curse. The turning of hearts is therefore to avert that curse. In Matthew 11, Jesus speaks to the Jews, the nation of Israel, about John the Baptist and the kingdom, but the Malachi passage gives the direct reason for Elijah's reconciling work.
And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.