I’m narrowing the answer to Malachi 4:6 and Luke 1:17 together, because John is not inventing the phrase; he is fulfilling Elijah-language about covenant restoration.

Main point:
It means that John’s ministry would produce repentance that restores covenant faithfulness across generations, beginning in the home and extending to the whole nation. It is not merely sentimental family healing. It is spiritual and moral restoration that shows itself in reconciled relationships, especially between fathers and children, as Israel is prepared for the coming of the Lord.

1. The key text

Malachi 4:5–6

“Behold, I will send you Elijah the prophet… And he will turn the hearts of fathers to their children and the hearts of children to their fathers…”

Luke 1:16–17

“And he will turn many of the children of Israel to the Lord their God… to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just…”

Luke is crucial because it interprets Malachi. The second half of Malachi’s phrase is paraphrased by Gabriel as:

• “the disobedient to the wisdom of the righteous”

That shows the meaning is broader than domestic affection alone. It is about repentance, moral restoration, and covenant alignment with God.

2. What “turn the hearts” means

In both Hebrew and Greek, the idea is not merely to feel warmly toward someone. It means to change one’s inner disposition, to be brought back, reoriented, reconciled.

So “turn the hearts of the fathers to the children” means:

• hardened, alienated, covenant-breaking people are brought back into right relationship
• family disorder is healed as part of national repentance
• one generation is reconciled to another under God’s covenant

This is why John’s preaching was, “Repent”. He was not running a family therapy ministry. He was calling Israel back to God, and that return to God would necessarily show up in the restoration of human relationships.

3. Why fathers and children?

In Malachi, the nation is spiritually corrupt. The book deals with covenant decay, priestly corruption, faithlessness, divorce, and social unrighteousness. So the language of fathers and children fits the setting well.

It points to at least three layers:

A. Literal family restoration

Where covenant life is broken, family life breaks with it. Repentance restores households, especially paternal responsibility and intergenerational faithfulness.

B. Intergenerational covenant continuity

Israel was meant to pass on the fear of the Lord from one generation to the next. When fathers’ hearts are turned to children, they again care about the covenant future of their offspring.

C. National preparation for Messiah

John prepares “a people made ready for the Lord.” That means he restores order, repentance, and covenant seriousness in Israel before the Messiah appears.

4. Was it only about literal fathers and children?

Not only that.

Some interpreters take “fathers” more broadly to include the forefathers/patriarchs of Israel, meaning that John would restore the people so that they come back into harmony with the faith of their ancestors. There is some theological sense in that reading, especially because John calls Israel back to true covenant fidelity.

But in the immediate wording of Malachi, and especially in the practical moral thrust of the book, the most natural sense includes actual generational reconciliation within the community. Then Luke expands the meaning by showing that this reconciliation is part of a larger repentance of the disobedient.

So the best reading is:

• yes, literal family relationships are included
• but the phrase is larger than family life
• it describes covenant restoration in Israel as a whole

5. Luke’s inspired interpretation is decisive

Gabriel does not quote Malachi woodenly. He interprets it:

• “turn many of the children of Israel to the Lord”
• “turn the hearts of the fathers to the children”
• “the disobedient to the wisdom of the righteous”
• “make ready for the Lord a prepared people”

That means the phrase is about:

1. conversion/repentance toward God
2. moral renewal
3. social and familial reconciliation
4. preparation for Messiah

So the family language is real, but it is embedded inside a larger revival-of-covenant-faithfulness theme.

6. What John was actually doing

John’s ministry did this by:

• calling people to repentance
• exposing hypocrisy
• confronting false security in ancestry
• demanding ethical fruit
• preparing Israel for the imminent arrival of the Lord

In other words, John “turned hearts” by calling people out of rebellion and into obedience. When fathers are truly turned to God, they are also turned rightly toward their children.

7. Practical theological meaning

This phrase teaches that real revival is not abstract.

It does not stop at:

• temple language
• prophetic excitement
• public religion

It reaches:

• the conscience
• the home
• the generations
• the moral structure of the covenant people

Where repentance is real, fathers do not remain distant, harsh, negligent, or spiritually dead toward their children. And children are not left in estrangement. God’s restoring work moves through the family as part of preparing a people for Himself.

Conclusion

“Turn the fathers’ hearts back to their children” means that through John’s Elijah-like ministry, God would bring about repentance that restores broken covenant relationships, especially across generations, so that Israel would be morally and spiritually prepared for the coming of Messiah.

So the phrase is:

• more than family warmth
• not less than family restoration
• fundamentally a picture of covenant repentance made visible in reconciled generations

If you want, I can next give you a full Hebrew-Greek word study of Malachi 4:6 and Luke 1:17, including the syntax and the patriarchs-vs-literal-fathers interpretive options.