It wasn't a miracle...
All the small specialist adaptations that allow emperors to survive where no other warm-blooded mammal could survive without artificial assistance are amazing.
But they are not miracles.
Emperors are birds. Flightless birds. With beaks, and other bird-like features. There are a number of species of penguins, but only one that we know of that can survive an Antartic winter. There probably were many other variants that came close to emperor's capability. There must have been some, because if the emperors did not have ancestors, they would not exist today.
Birds, and therefore penguins, descended from something that was a dinosaur with feathers 65 million years ago. These adaptations happen over timescales we cannot readily understand. But scientists have discovered countless examples of such adaptations in the fossil record and more recently in living organisms over timescales close to a human life-span.
So emperors are not a miracle, they are an example of the amazing power of natural selection to provide organisms with features that can fill any niche however small, however hostile to the adaptations of most higher species.