What does Daniel 5:24 mean?

In this verse Daniel finally addresses the subject for which King Belshazzar summoned him (Daniel 5:16). Babylonian royalty were enjoying an alcohol-soaked party, including the use of sacred Jewish religious vessels (Exodus 30:22–29; Daniel 1:1–2) for drinking toasts to idols (Daniel 5:1–4). This was interrupted by disembodied fingers making letters on the wall (Daniel 5:5). This horrified the king and baffled his other advisors (Daniel 5:6–9). Yet when Daniel first arrived, he did not immediately explain the words. Instead, he describes the humbling experience of a prior king, Nebuchadnezzar (Daniel 4:28–33; 5:18–21). Daniel, likely eighty years old and still a captive under the empire of Babylon, uses that history as a foundation to upbraid Belshazzar for arrogance and blasphemy (Daniel 5:22–23).

Now, Daniel explains that the sign is from his God: the Most High God of Israel. The Lord delivered this message, in part, because of Belshazzar's recent sins. But the writing on the wall has more to do with God's perfect timing than a single act of idolatry driving Him into action. Daniel's speech makes it clear that Belshazzar hadn't followed God prior to this event. The idolatry and disrespect of the evening were just the latest effects of his rejection of the Lord.

Sometimes, God chooses to let an unbeliever's pride and blasphemy build up to a peak before He unleashes judgment. In the New Testament, King Herod was already known for wickedness and unbelief. When he delivered a speech and accepted praise as a god, the Lord struck him with a horrific and fatal disease (Acts 12:20–23). Belshazzar's fate is being announced in a moment where he has no excuse—to the Lord or even to other men—about the depths of his sin.