Ezekiel 21:5

That all flesh may know that I the LORD have drawn forth my sword out of his sheath: it shall not return any more.

The sword is the calamity coming upon Judah and Jerusalem through the Babylonian siege. It is unsheathed by the Lord's command to put an end to human insolence and disobedience. This happens when men in presumption and defiance, like Belshazzar, pass the boundary and limit of grace and exhaust God's longsuffering forbearance. The judgment comes in the midst of mirth, feasting, and forgetfulness of God, when transgression will no longer be tolerated and God interferes to repress the overflowing tide of iniquity.

The act answers the prayers of God's people for God to work because His law has been made void. Its purpose is that all flesh may know that the Lord is acting and see that He is God. Once drawn from its sheath, the sword of judgment will not return or be put away until the judgment is carried out, but remains.