Daniel 5:29

Belshazzar . . . clothed Daniel with scarlet--To come from the presence of a prince in a dress presented to the wearer as a distinction is still held a great honor in the East. Daniel was thus restored to a similar rank to what he had held under Nebuchadnezzar (Dan 2:48). Godly fidelity which might be expected to bring down vengeance, as in this case, is often rewarded even in this life. The king, having promised, was ashamed before his courtiers to break his word. He perhaps also affected to despise the prophecy of his doom, as an idle threat. As to Daniel's reasons for now accepting what at first he had declined, compare Note, see on Dan 5:17. The insignia of honor would be witnesses for God's glory to the world of his having by God's aid interpreted the mystic characters. The cause of his elevation too would secure the favor of the new dynasty (Dan 6:2) for both himself and his captive countrymen. As the capture of the city by Cyrus was not till near daylight, there was no want of time in that eventful night for accomplishing all that is here recorded. The capture of the city so immediately after the prophecy of it (following Belshazzar's sacrilege), marked most emphatically to the whole world the connection between Babylon's sin and its punishment.

— Jamieson-Fausset-Brown Commentary (public domain)