Adam Clarke on Isaiah 21:5

Prepare the table "The table is prepared" - In Hebrew the verbs are in the infinitive mood absolute, as in Eze 1:14 : "And the animals ran and returned, רצוא ושוב ratso veshob, like the appearance of the lightning;" just as the Latins say, currere et reverti, for currebant et revertebantur. See Isa 33:11 (note), and the note there.

Arise, ye princes, and anoint the shield - Kimchi observes that several of the rabbins understood this of Belshazzar's impious feast and death. The king of a people is termed the shield, because he is their defense. The command, Anoint the shield, is the same with Anoint a new king. Belshazzar being now suddenly slain, while they were all eating and drinking, he advises the princes, whose business it was, to make speed and anoint another in his stead.