Q. Why did God reveal future events to Nebuchadnezzar?
Here is what I say about that in my study guide to Daniel and Revelation. (You can read the guide online or download it for free at this link.)
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(p. 28, about Nebuchadnezzar’s dream of the statue) Nebuchadnezzar was wondering about the future of his empire. (Daniel notes, “As Your Majesty was lying there, your mind turned to things to come.”) The take-home message of the dream is that his empire isn’t going to last forever. In fact, in the foreseeable future it will be overrun by a rival empire. Daniel’s task, as God’s representative, is to challenge Nebuchadnezzar to accept this fact and humble himself before the “Lord of kings.”
(p. 30, about the statue that Nebuchadnezzar built) God gave Nebuchadnezzar an inspired dream about a statue made of different materials. The interpretation was that the Babylonian empire (the statue’s head of gold) wouldn’t last forever; instead, it would ultimately be replaced by a kingdom that the “God of heaven” would set up. When Nebuchadnezzar first heard Daniel interpret his dream, he was so amazed that he “fell prostrate before” him and “paid him honor.” But now he’s had a change of heart. He makes a statue entirely out of gold, to assert—in the language of the dream, and directly contradicting God’s word—that his empire will last forever. He gathers provincial officials from all over his empire and demands that they “fall down” and “worship” this statue. (These are exactly the same Aramaic words used to describe what Nebuchadnezzar did for Daniel; the king wants his empire to be on the receiving end this time!)
(pp. 31–32, same episode) Shadrach, Meshach, and Abednego tell the king that if their God is able to deliver them, he will, but that even if he doesn’t, they won’t serve the Babylonian gods or worship the statue. Their obedience wasn’t conditional on their deliverance. Nebuchadnezzar recognizes this and praises them for being “willing to give up their lives rather than serve or worship any god except their own God.” … In Daniel’s song of praise in the previous story, he said that “wisdom and power” belonged to God. When Daniel interpreted Nebuchadnezzar’s dream, the king acknowledged God as a “revealer of mysteries”—a God of wisdom. Now he acknowledges that this God has “rescued his servants” and must also be a God of power. He forbids anyone in his empire to say anything against “the God of Shadrach, Meshach and Abednego.”
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So, to answer your question, God revealed future things to Nebuchadnezzar to get him to realize that his empire would not last forever so that he would humble himself and acknowledge God as the true ruler of the world.