Because it shows that there will be survivors after the second coming of the Messiah, which will:
1. Be few in number, but will multiply and become mighty nations.
2. Will be subjected to sin and death.
3. And will serve the Messiah and the people of God.
Then everyone who survives of all the nations that have come against Jerusalem shall go up year after year to worship the King, Yehovah of armies, and to keep the Feast of Tabernacles. And if any of the families of the earth do not go up to Jerusalem to worship the King, Yehovah of armies, there will be no rain on them. And if the family of Egypt does not go up and present themselves, then on them there shall be no rain; which shall be the plague with which Yehovah afflicts the nations that do not go up to keep the Feast of Tabernacles. (Zechariah 14:16-18)
I pursued my enemies and overtook them, And I did not turn back until they were consumed. I shattered them, so that they were not able to rise; They fell under my feet. For You have girded me with strength for battle; You have subdued under me those who rose up against me. You have also made my enemies turn their backs to me, And I destroyed those who hated me. They cried for help, but there was none to save, Even to Yehovah, but He did not answer them. Then I beat them fine as the dust before the airflow; I emptied them out as the mire of the streets. You have delivered me from the contentions of the people; You have placed me as head of the nations; A people whom I have not known serve me. As soon as they hear, they obey me; Foreigners submit to me. Foreigners fade away, And come trembling out of their fortresses. Yehovah lives, and blessed be my rock; And exalted be the God of my salvation, The God who executes vengeance for me, And subdues peoples under me. (Psalm 18:37-47)
For Yehovah will have compassion on Jacob and will again choose Israel, and will set them in their own land, and sojourners will join them and will attach themselves to the house of Jacob. And the peoples will take them and bring them to their place, and the house of Israel will possess them in the land of Yehovah as male and female servants. They will take captive those who were their captors, and rule over those who oppressed them. (Isaiah 14:1-2)
See, Yehovah is going to lay waste the earth and devastate it; he will ruin its face and scatter its inhabitants— it will be the same for priest as for people, for the master as for his servant, for the mistress as for her servant, for seller as for buyer, for borrower as for lender, for debtor as for creditor. The earth will be completely laid waste and totally plundered. Yehovah has spoken this word. The earth dries up and withers, the world languishes and withers, the heavens languish with the earth. The earth is defiled by its people; they have disobeyed the laws, violated the statutes and broken the aeonial covenant. Therefore a curse consumes the earth; its people must bear their guilt. Therefore earth’s inhabitants are burned up, and very few are left. (Isaiah 24:1-6)