What does Daniel 5:18 mean?

Daniel was summoned to interpret a terrifying incident where King Belshazzar saw disembodied fingers writing on the wall (Daniel 5:1–5). Daniel's first comments are to dismiss the king's offer of reward and express confidence that he can explain what has happened (Daniel 5:17). Yet he speaks as if he already knows the answer. Here, he begins speaking about a prior king, Nebuchadnezzar. This is meant to set up Daniel's scathing criticism of Belshazzar as an unrepentant, profane, arrogant man (Daniel 5:23).

Nebuchadnezzar's fame was known far and wide. His glory was unprecedented. He beautified Babylon and his palace. He launched many building projects and commanded a powerful army. No one could doubt his authority over all his subjects. But he owed his greatness, glory, and majesty to God. Near the end of his life, he was humbled by the Lord and forced to admit his own need (Daniel 4:34–37).

This passage clearly shows that Belshazzar rejected the Most High God and refused to acknowledge His Lordship. Belshazzar praised heathen deities. His faith was placed in idols who did not see, hear, or do him any good. Romans 1:22–23 indicts the unbeliever who acts like Belshazzar: "claiming to be wise, they became fools, and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things."