Ezekiel 21:25

And thou, profane wicked prince of Israel, whose day is come, when iniquity shall have an end,

The address is directed to Zedekiah as the profane wicked prince of Israel whose day of final reckoning had come. He is called by that name because he broke his solemn oath and covenant made before God to render allegiance to the king of Babylon. That rebellion and breach of his oath brought judgment upon him.

The announcement means his day had come and the earthly theocracy was to end, with the diadem removed and the crown taken off. The overturning it foretells was fulfilled three times: when Babylon fell to Medo-Persia, when Medo-Persia fell to Greece, and when Greece gave way to Rome. After that the throne of the Lord is removed from this world and shall be no more until He come whose right it is.

Judah would have no king again until Christ, the rightful ruler, established His kingdom. That coming One whose right it is is Jesus, to whom God will give the throne of His father David to reign over the house of Jacob forever. That giving of the kingdom takes place at the end of this world and the beginning of the world to come, so no theocratical government is to be set up on earth now.