IT turns out that reason has less of a hold on religion and science that one might suppose; or, at least, on Judaism and physics.
In Jewish legal lingo, a “decree” is a rule that runs against reason. The classic decree is that of the Red Cow. Its ashes, ritually prepared, contaminate its preparers; at the same time, these ashes purify the impure people on whom the ashes, mixed with spring water, are sprinkled.
Same object: ashes.
Two diametrically opposed results: impurity and purity.
That’s a “decree.”