From my studies; "the day of the lord" is every national event when Yah exercises fierce judgment against His enemies and (re)established His sovereign rule, which leads to peace/rest.
So the judgment against Jerusalem in the BCs was the day of the lord.
...and the judgment against Jerusalem in 70AD was the day of the lord.
...and the prophetic judgment against Esau/Edom (in Obadiah) was/will be the day of the lord before and again.
...and the final judgment against the armies of the world will be the day of the lord.
It is His day, when He puts down all rebellion, and whoever is on His side is rewarded while those who are against him are defeated.
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The history of mankind is cyclical until all is fulfilled.
Ecclesiastes 1:9
"What has been is what will be; what has been done is what will be done. There is nothing new under the sun."
I've ran across other people that hold that view. I don't hold that view, and if you read Malachi 4 from the king James bible, read all of it, but pay close attention to verse 4. This is one of many reasons I don't hold that view.
Mal 4:1 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.
Mal 4:2 But unto you that fear my name shall the Sun of righteousness arise with healing in his wings; and ye shall go forth, and grow up as calves of the stall.
Mal 4:3 And ye shall tread down the wicked; for they shall be ashes under the soles of your feet in the day that I shall do this, saith the LORD of hosts.
Mal 4:4 Remember ye the law of Moses my servant, which I commanded unto him in Horeb for all Israel, with the statutes and judgments.
Mal 4:5 Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD:
Mal 4:6 And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
Malachi 4:4 is bringing attention to the covenant God made with Israel and without saying a word about the consequences of not keeping that covenant (Deu 28:15), he moves on to verse 5 and talks about "the great and dreadful day of the Lord".
Deu 28:15 But it shall come to pass, if thou wilt not hearken unto the voice of the LORD thy God, to observe to do all his commandments and his statutes which I command thee this day; that
all these curses shall come upon thee, and overtake thee:
From Malachi chapter 4 we can see that "the day of the Lord" is a specific time, a time that wont happen until after Elijah (John the Baptist) comes preaching repentance to Israel.
But the MOST INTERESTING thing in chapter 4 to me is that "the
Sun of righteousness" comes with healing in his wings to deliver the righteous of Israel BEFORE the great and dreadful day comes.
So to me, the DAY of the Lord is when the SUN of righteousness rises.