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.
The Prophet sets this threat against God's enemies to answer those who slander Him, claiming He has stopped being Judge. The ungodly will be like stubble in a furnace, a common Scripture image, and the day of the Lord will consume them entirely, leaving neither root nor branch. The demonstrative 'Behold' marks certainty.
AI summary
Commenting on Malachi 4:1-6
This is doubtless intended for a solemn conclusion, not only of this prophecy, but of the canon of the Old Testament, and is a plain information that they were not to expect any more sayings nor writing by divine inspiration, any more of the dictates of the Spirit of prophecy, till the beginning of the gospel of the Messiah, which sets aside the Apocrypha as...
Commenting on Malachi 4:4-6
And he shall turn the heart of the fathers to the children,.... Or "with" the children, as Kimchi; and Ben Melech observes, that is put for and so in the next clause: and the heart of the children to their fathers; or "with" their fathers; that is, both fathers and children: the meaning is, that John the Baptist should be an instrument of converting many...