Chapter 4 is a little bit different. In this instance, the order of the illustrating event and Nebuchadnezzar's proclamation are reversed. Indeed, very early on in verses 1-3, Nebuchadnezzar writes a decree to the entire nation, saying,
"Nebuchadnezzar the king, unto all people, nations, and languages, that dwell in all the earth; Peace be multiplied unto you. I thought it good to shew the signs and wonders that the high God hath wrought toward me. How great are his signs! and how mighty are his wonders! his kingdom is an everlasting kingdom, and his dominion is from generation to generation."
With that declaration in mind, we turn to the events of the story. Nebuchadnezzar goes on in his decree to discuss then reason why he feels that God is the most High in the first place. It starts just as it did in Chapter 2, with a dream.
This dream Nebuchadnezzar remembers, but he doesn't understand it. And neither do any of his wise men. Nebuchadnezzar is afraid because of the contents of the dream.
So since you're probably curious, the dream went something like this. There was a great tree which was beautiful and was providing food and shelter for many. And then an angel comes down and asks that it be hewed down, but the stump can remain. In the most relevant portion, the angel declares,
"Let it be wet with the dew of heaven, and let his portion be with the beasts in the grass of the earth: Let his heart be changed from man's, and let a beast's heart be given unto him; and let seven times pass over him."
Nebuchadnezzar in his terror, remembers that there was this guy, in whom was the spirit of the holy god(s). (Whether you have gods or God will depend upon your translation. In the Aramaic, the plural form was often used for emphasis, making this statement a little bit arbitrary.)
Nebuchadnezzar calls in Daniel, and Daniel is said to be troubled for an hour, and was in one of my favorite KJV words, "astonied." And Nebuchadnezzar has apparently softened at some point because he tells Daniel not to worry about the dream or the interpretation.
At which point, Daniel explains the dream. In verses 24-27,
"This is the interpretation, O king, and this is the decree of the most High, which is come upon my lord the king: That they shall drive thee from men, and thy dwelling shall be with the beasts of the field, and they shall make thee to eat grass as oxen, and they shall wet thee with the dew of heaven, and seven times shall pass over thee, till thou know that the most High ruleth in the kingdom of men, and giveth it to whomsoever he will. And whereas they commanded to leave the stump of the tree roots; thy kingdom shall be sure unto thee, after that thou shalt have known that the heavens do rule. Wherefore, O king, let my counsel be acceptable unto thee, and break off thy sins by righteousness, and thine iniquities by shewing mercy to the poor; if it may be a lengthening of thy tranquillity."
The dream stands as a warning against Nebuchadnezzar's pride. It is asking him to consistently acknowledge that it is God who creates his own kingdoms. This is what the Most High decrees. And obviously what the most High decrees, will inevitably come to pass.
In verses 28-33, it does,
"All this came upon the king Nebuchadnezzar. At the end of twelve months he walked in the palace of the kingdom of Babylon. The king spake, and said, Is not this great Babylon, that I have built for the house of the kingdom by the might of my power, and for the honour of my majesty? While the word was in the king's mouth, there fell a voice from heaven, saying, O king Nebuchadnezzar, to thee it is spoken; The kingdom is departed from thee. And they shall drive thee from men, and thy dwelling shall be with the beasts of the field: they shall make thee to eat grass as oxen, and seven times shall pass over thee, until thou know that the most High ruleth in the kingdom of men, and giveth it to whomsoever he will. The same hour was the thing fulfilled upon Nebuchadnezzar: and he was driven from men, and did eat grass as oxen, and his body was wet with the dew of heaven, till his hairs were grown like eagles' feathers, and his nails like birds' claws."
And so we see that the Lord's prophecies come true because He's God and is sovereign at all times. And Nebuchadnezzar actually states this fact again, and praised the Lord God of Heaven, the chapter ends in verses 34-37,
"And at the end of the days I Nebuchadnezzar lifted up mine eyes unto heaven, and mine understanding returned unto me, and I blessed the most High, and I praised and honoured him that liveth for ever, whose dominion is an everlasting dominion, and his kingdom is from generation to generation: And all the inhabitants of the earth are reputed as nothing: and he doeth according to his will in the army of heaven, and among the inhabitants of the earth: and none can stay his hand, or say unto him, What doest thou? At the same time my reason returned unto me; and for the glory of my kingdom, mine honour and brightness returned unto me; and my counsellors and my lords sought unto me; and I was established in my kingdom, and excellent majesty was added unto me. Now I Nebuchadnezzar praise and extol and honour the King of heaven, all whose works are truth, and his ways judgment: and those that walk in pride he is able to abase."