This image's head was of fine gold, his breast and his arms of silver, his belly and his thighs of brass,
This image's head was of fine gold. On ancient coins states are often represented by human figures. The head and higher parts signify the earlier times; the lower, the later times. The metals become successively baser and baser, implying the growing degeneracy from worse to worse. Hesiod, 200 years before Daniel, had compared the four ages to the four metals in the same order: the idea is sanctioned here by Holy Writ. It was perhaps one of those fragments of revelation among the pagan, derived from the tradition as to the fall of man. The metals lessen in specific gravity as they go downward: silver is not so heavy as gold, brass not so heavy as silver, and iron not so heavy as brass, the weight thus being arranged in the reverse of stability (Tregelles).
Nebuchadnezzar derived his authority from God, not from man, nor as responsible to man. On the other hand, Darius the Persian king was so far dependent on his satraps and nobles that he could not deliver Daniel from the princes, though "he set his heart on Daniel to deliver him; and he laboured until the going down of the sun to deliver him" (Daniel 6:14-15); contrast Daniel 5:18-19, as to Nebuchadnezzar's power from God, "The most high God gave Nebuchadnezzar, thy father, a kingdom and majesty, and glory, and honour ... whom he would he slew, and whom he would he kept alive" (cf. Ezra 7:14, "Thou (Ezra) art sent of the king and of his seven counselors;" Esther 1:13-16).
Graeco-Macedonia betrays its deterioration in its divisions, not united as Babylon and Persia were. Iron is stronger than brass, but inferior in other respects; so Rome was hardy and strong to tread down the nations; but was less kingly, and showed its chief deterioration in its last state. Each successive kingdom incorporates its predecessor (cf. Daniel 5:28). Power that in Nebuchadnezzar's hands was a God-derived (Daniel 2:37-38) autocracy, in the Persian king's was a rule resting on his nobility of person and birth, the nobles being his equals in rank, but not in office; in Greece, an aristocracy not of birth, but individual influence; in Rome, lowest of all, dependent entirely on popular choice, the emperor being appointed by popular military election.