For through Isaiah, “this is what YHWH says: 'As when grape juice is found in the cluster, and someone says, 'do not destroy it, for a blessing is in it,' so will I do on account of my servants, so as not to destroy them all. And I will bring forth an offspring out of Jacob, and out of Judah the one to inherit my mountains; and my chosen ones will inherit it, and my servants will dwell there.'” 1
And again: “Look! My servants will eat, but you will be hungry. Look! My servants will drink, but you will be thirsty. Look! My servants will rejoice, but you will be ashamed.” 2
By saying “my servants,” he is rebuking the ones to whom he is speaking, and creating a promise that there would be a clear distinction between YHWH’s servants and them.
And again, he says: “You will leave your name as a curse to my chosen ones. For my Lord YHWH will put you to death, and will call his servants by another name; so that he who blesses himself in the earth will bless himself by the God of truth, and the one swearing in the earth will swear by the God of truth; for the former troubles are forgotten, because they are concealed from my eyes.” 3
And so the purpose of destruction is to clear out the bad, and to bring forth a remnant; a cleaned, refined people.
After your ancestors returned from Babylon and restored the Temple, YHWH again found fault with them, through the mouth of Malachi, whose name means “My Messenger.”
YHWH said: “Look! I am sending my messenger, and he prepares the way before me; and suddenly the Lord whom you are seeking will come to his Temple, and the messenger of the covenant in whom you take delight. Look! He is coming, says YHWH of hosts.
But who will endure the day of his coming? And who will stand when he appears? For he is as the fire of a refiner, and as the soap of a cleaner.” 4
Speaking of that time, YHWH says, “I will come near to you for judgment, and I will be a swift witness against the sorcerers, and against the adulterers, and against false swearers, and against those who oppress the worker's wage, the widow, and the orphan, and those who turn aside from the foreigner, and do not fear me, says YHWH of hosts.” 5
Now, what is the means by which he would make a distinction, and call out his true servants? Malachi says, “Then each man who feared YHWH spoke with his neighbor, and YHWH paid attention and heard, and a book of remembrance was written before him, for those fearing YHWH and for the ones who esteemed his name. And they will be mine, says YHWH of hosts, in the day I make a treasured possession; and I will spare them, as when a man spares his own son who serves him. And you will return, and you will discern between the righteous and the wicked, between one serving God, and one not serving him.
For look! The day is coming, burning as the stove, and all of the arrogant and everyone practicing wickedness will become stubble, and the day that is coming will burn them up, says YHWH of hosts, and will not leave them either root or branch.” 6
By saying “treasured possession,” he is using the same language he used to describe Israel. For YHWH told Moses to speak to Israel and say: “If you will carefully listen to my voice, and keep my covenant, then you will be a treasured possession to me out of all the peoples. For all the earth is mine, but you will be a kingdom of priests and a holy nation to me.” 7
But since YHWH is already speaking to Israel through Malachi, his later “treasured possession” must be a remnant of Israel. YHWH first makes them as his special people, and then spares them as sons in the day of his anger.