Some passages describe blessed and wretched outcomes so vividly that the reader perceives more than labels for reward and punishment. Descriptions of peace and delight awaken hope; deprivation and torment convey warning and fear.
Calling these accounts mere imagination would erase their intended reference to the hereafter. Conversely, attempting to specify every unseen detail where revelation is silent would exceed the evidence.
The rhetorical gain lies in making the message clearer, more memorable, and more compelling to both thought and feeling.