John said he wasn't Elijah,and then quote first chapter of Malachi.
https://www.biblegateway.com/passage/?search=Malachi+1&version=NIV
How does this fit? Consider the forced conversion of the Edomites.
4 Edom may say, “Though we have been crushed, we will rebuild the ruins.”
But this is what the Lord Almighty says: “They may build, but I will demolish. They will be called the Wicked Land, a people always under the wrath of the Lord. 5 You will see it with your own eyes and say, ‘Great is the Lord—even beyond the borders of Israel!’