one decree - There can be no second one reversing the first (Est 4:11).
corrupt - deceitful.
till the time be changed - till a new state of things arrive, either by my ceasing to trouble myself about the dream, or by a change of government (which perhaps the agitation caused by the dream made Nebuchadnezzar to forebode, and so to suspect the Chaldeans of plotting).
tell ... dream, and I shall know ... ye can show ... interpretation - If ye cannot tell the past, a dream actually presented to me, how can ye know, and show, the future events prefigured in it?