Daniel 5:2 (ESV)

2 Belshazzar, when he tasted the wine, commanded that the vessels of gold and of silver that Nebuchadnezzar his father had taken out of the temple in Jerusalem be brought, that the king and his lords, his wives, and his concubines might drink from them.

When the revelry increases and the wine starts having its influence over Belshazzar and his company, the king issues a striking command. A command showing that the wine has gained the upper hand over him. This is because the command he gives was unheard of in those days, even for someone who worships idols. Those who worshipped other gods in those days were always afraid to mock another god. If you did, that god might get angry with you and you never knew what would happen. That is why Nebuchadnezzar and his successors safely guarded the things they took from the Lord's temple in Jerusalem in a separate place and did not use them. But Belshazzar now orders the gold and silver cups from the temple in Jerusalem to be used. These beautiful cups, which were dedicated to the Lord and his service, are to add zest to the celebration.