After King Solomon, Israel was divided into two nations. Israel to the north and Judah to the South.
It was 930 BC when they divided and the northern kingdom Israel met its end in 722 BC. Judah would later fall and Jerusalem would be ransacked and burned in 586 BC.
So the importance of this prophecy is because Israel was more than one nation for many years.
Ezekiel 37:21-22 – 21 and say to them, ‘This is what the Sovereign LORD says: I will take the Israelites out of the nations where they have gone. I will gather them from all around and bring them back into their own land. 22 I will make them one nation in the land, on the mountains of Israel. There will be one king over all of them and they will never again be two nations or be divided into two kingdoms.
There will be one King. That King, will be the King of Kings and Lord of Lords . The Messiah the Jews have rejected for 2000 years.
Zechariah 12:10 – 10 “And I will pour out on the house of David and the inhabitants of Jerusalem a spirit of grace and supplication. They will look on [me, the one they have pierced, and they will mourn for him as one mourns for an only child, and grieve bitterly for him as one grieves for a firstborn son.
Jesus will rule and reign for a thousand years. The devil will be bound and thrown into the bottomless pit for a thousand years. All of those who loved the Lord and are part of the first resurrection will rule and reign with Him.
The House of Israel will finally have their King under a unified nation.