What does Malachi 3:4 mean?

“Behold, I send my messenger, and he will prepare the way before me; and the Lord, whom you seek, will suddenly come to his temple; and the messenger of the covenant, whom you desire, behold, he comes!” says Yahweh of Armies.

“But who can endure the day of his coming? And who will stand when he appears? For he is like a refiner’s fire, and like launderers’ soap;

and he will sit as a refiner and purifier of silver, and he will purify the sons of Levi, and refine them as gold and silver; and they shall offer to Yahweh offerings in righteousness.

I will come near to you to judgment; and I will be a swift witness against the sorcerers, and against the adulterers, and against the perjurers, and against those who oppress the hireling in his wages, the widow, and the fatherless, and who deprive the foreigner of justice, and don’t fear me,” says Yahweh of Armies.

“For I, Yahweh, don’t change; therefore you, sons of Jacob, are not consumed.

From the days of your fathers you have turned away from my ordinances, and have not kept them. Return to me, and I will return to you,” says Yahweh of Armies. “But you say, ‘How shall we return?’