The symbols of the prophecy are the key to understanding it.
The context clearly indicates a siege;
The city involved is clearly Jerusalem;
The prophecy is given for "iniquity" (both of Israel and of Judah);
The prophecy for Israel is given before that of Judah, indicating their order; and
The iniquities are not equal, as indicated by Ezekiel's left versus right sides.
The iniquity of Israel is so often mentioned throughout the books of the kings as to be unmistakable.
1Ki 14:16 And he shall give Israel up because of the sins of
Jeroboam, who did sin, and who made Israel to sin.
1Ki 15:26 And he did evil in the sight of the LORD, and walked in the
way of his father, and in his sin wherewith he made Israel to sin.
1Ki 15:34 And he did evil in the sight of the LORD, and walked in the
way of Jeroboam, and in his sin wherewith he made Israel to
sin.
1Ki 16:2 Forasmuch as I exalted thee out of the dust, and made thee
prince over my people Israel; and thou hast walked in the way of
Jeroboam, and hast made my people** Israel to sin**, to provoke me to anger with their sins;
1Ki 16:19 For his sins which he sinned in doing evil in the sight of
the LORD, in walking in the way of Jeroboam, and in his sin which
he did, to make** Israel to sin**.
1Ki 16:26 For he walked in all the way of Jeroboam the son of
Nebat, and in his sin wherewith he made Israel to sin, to
provoke the LORD God of Israel to anger with their vanities.
1Ki 21:22 And will make thine house like the house of Jeroboam the
son of Nebat, and like the house of Baasha the son of Ahijah, for
the provocation wherewith thou hast provoked me to anger, and made
Israel to sin.
1Ki 22:52 And he did evil in the sight of the LORD, and walked in the
way of his father, and in the way of his mother, and in the way of
Jeroboam the son of Nebat, who made Israel to sin:
2Ki 3:3 Nevertheless he cleaved unto the sins of Jeroboam the son
of Nebat, which made Israel to sin; he departed not therefrom.
2Ki 10:29 Howbeit from the sins of Jeroboam the son of Nebat, who
made Israel to sin, Jehu departed not from after them, to wit, the golden calves that were in Bethel, and that were in Dan.
2Ki 10:31 But Jehu took no heed to walk in the law of the LORD God of
Israel with all his heart: for he departed not from the sins of
Jeroboam, which made Israel to sin.
2Ki 13:2 And he did that which was evil in the sight of the LORD, and
followed the sins of Jeroboam the son of Nebat, which made
Israel to sin; he departed not therefrom.
2Ki 14:24 And he did that which was evil in the sight of the LORD: he
departed not from all the sins of Jeroboam the son of Nebat, who
made Israel to sin.
2Ki 15:9 And he did that which was evil in the sight of the LORD, as
his fathers had done: he departed not from the sins of Jeroboam the
son of Nebat, who made Israel to sin.
2Ki 15:18 And he did that which was evil in the sight of the LORD: he
departed not all his days from the sins of Jeroboam the son of
Nebat, who made Israel to sin.
2Ki 15:24 And he did that which was evil in the sight of the LORD: he
departed not from the sins of Jeroboam the son of Nebat, who
made Israel to sin.
2Ki 15:28 And he did that which was evil in the sight of the LORD: he
departed not from the sins of Jeroboam the son of Nebat, who
made Israel to sin.
2Ki 23:15 Moreover the altar that was at Bethel, and the high place
which Jeroboam the son of Nebat, who made Israel to sin, had
made, both that altar and the high place he brake down, and burned the
high place, and stamped it small to powder, and burned the grove.
It is plain to see that Jeroboam caused Israel to sin, and that this was a significant event. What did he do? He built the golden calves at Dan and at Bethel and caused the people to worship them instead of going to Jerusalem to worship God. He was afraid they would return to serving king Rehoboam, instead of himself, if they returned to Jerusalem for worship as had been their custom.
The fact that they had turned away from the worship of God in Jerusalem, and had turned away from God's temple, wonderfully built by King Solomon to the glory and honor of God, is what brought God to allow the destruction of that beautiful temple 390 years later, as indicated in the prophecy. The years were not years of punishment, they were years of probation before the punishment would come.
However, as the Bible places greater significance to the right side than to the left, the prophecy indicates that Judah's sin would be greater yet. In spite of this fact, much less appears to be said about it--in the Old Testament, at least. The one text specifically mentioning it seems ominous:
"The sin of Judah is written with a pen of iron, and with the point of
a diamond: it is graven upon the table of their heart, and upon the
horns of your altars" (Jeremiah 17:1)
When one thinks of a "pen of iron," what comes to mind?
In Jesus' day, the remnants of the 10 tribes (the Northern Kingdom / Israel) had become the hated Samaritans. They had intermarried with the surrounding nations, and, thinking them impure, the Jews (Judah) would not even permit them to enter the temple. Thus it was Judah for whom Christ labored.
And it was Judah who rejected Christ. The "pen of iron" is a fitting description for the nails which pierced Christ; and the "point of a diamond" is a fitting symbol for the spear that would pierce his side.
Just forty years later, the second temple was also destroyed. Not only had Judah rejected the true worship of God; they had murdered him. Their probationary time was much less, and their punishment came more swiftly and in greater severity.
Thus, Ezekiel's prophecy foretold both apostasies, and both destructions of the temple that would come on account of them.