Because of the insanity that will come upon him, Nebuchadnezzar will look more like an animal than a human. He will eat like an ox. The people will adapt to this and give him the food that is suitable for animals. He is going to look like an animal in human form—that is how bad things will get. It will last for seven periods of time. We do not know how long those periods were. During that time he has to come to the acknowledgment that it is not he who is the great ruler but that the Lord has all the power in heaven and on earth and that he can never be more than a viceroy under the Lord. Also his kingship is given by the Lord who governs everything. The mighty Nebuchadnezzar needs to acknowledge this reality.
Through this punishment, the Lord shows what Nebuchadnezzar was actually doing. He was engaged in the service of the devil. He was serving the kingdoms of the two beasts that we read about in Revelation 13:1–18. The kingdoms of the beast from the sea and the beast from the earth are together in the service of the dragon. It represents a truly diabolical, beastly kingdom that stands in opposition to the kingdom of Christ. In his self-exaltation, Nebuchadnezzar is acting like a beast. His kingdom actually causes the dehumanization of people. People miss out on their real goal, which is that they would live in the image of God. The Lord shows that this self-exaltation cannot and will not last.
25 that you shall be driven from among men, and your dwelling shall be with the beasts of the field. You shall be made to eat grass like an ox, and you shall be wet with the dew of heaven, and seven periods of time shall pass over you, till you know that the Most High rules the kingdom of men and gives it to whom he will.