HERE is a logical order to the issues that are raised in Ezekiel 21. As you probably know, God chose a people for Himself out of the greater population of this world. And, He chose them for a specific purpose. He chose the Jews. It was through His covenants with Abraham, Isaac and Jacob that God solemnized His selection. He had purposed to separate the Jews for a few primary reasons. Most importantly, God intended to send the Messiah, the Savior of the world, through this ethnic group. In preparation for the coming of the Christ, it was God's desire to keep His people holy and separate. Through the implementation of the Law of Moses, God intended to declare His own name and character to and through the Jews. This is where a big problem arose. The Jews not only fell short in their assignment, they utterly rebelled against it.
If you read Ezekiel 21 carefully, you will notice many references to the sword of the Lord. Now, the sword of God (in this case) was being wielded most obviously by the Chaldeans, nevertheless, the program of justice against the Jews (and others) was God’s work. The Jews had squandered the opportunities that God had given them. His people had sinned continually. God was angry. God warned the Jews through the words of many prophets, including Ezekiel. Judgment was on the way. Yet, there is one more issue to view here, which we have not yet taken in hand, and that is the disposition of the prophet as he fulfilled his duties.
Very specifically, God commanded Ezekiel to "sigh, cry and howl... and to smite upon his thigh" (Ezekiel 21:6 & 12). This is significant. This was more than just a didactic tool. In Ezekiel 21:10 the question is asked, "Should we make mirth?" In other words, as God sharpens His sword in preparation for the slaughter of His wicked enemies, should those who have knowledge of His coming judgment respond lightly to that reality? It's a rhetorical question. An appropriate response from Ezekiel would include sadness, mourning & weeping... both for the wicked, and before them.