Malachi 4:1-6: For, behold, the day cometh, that shall burn as an oven; and all the proud, yea, and all that do wickedly, shall be stubble: and the day that cometh shall burn them up, saith the LORD of hosts, that it shall leave them neither root nor branch.
But to you who fear My name
The Sun of Righteousness shall arise
With healing in His wings;
And you shall go out
And grow fat like stall-fed calves.
3 You shall trample the wicked,
For they shall be ashes under the soles of your feet
On the day that I do this,”
Says the Lord of hosts.
4 “Remember the Law of Moses, My servant,
Which I commanded him in Horeb for all Israel,
With the statutes and judgments.
5 Behold, I will send you Elijah the prophet
Before the coming of the great and dreadful day of the Lord.
6 And he will turn
The hearts of the fathers to the children,
And the hearts of the children to their fathers,
Lest I come and strike the earth with a curse.”
The day of the Lord will be a time of fierce judgment on the earth, and the wicked will be burned like stubble. In scripture, "fire" is often associated with judgment, for it is a symbol of the holy wrath of God.