What does Kant entail when he speaks of his epistemological 'Copernican Revolution'?

Kant's 'Copernican Revolution' in epistemology suggested that cosmology, particle physics, theology and free will/determinism claims involve questions that are naturally raised by the structure of the mind, but owing to the nature of how the mind interacts and reconfigures the data from external world, the nature of this external world is unknowable to us. As a result, all forms of traditional theoretical metaphysical objects of enquiry rest on a fundamental mistake and cannot be objectively known in themselves. That said, the metaphysical concepts, God, the afterlife, the soul and free will still have a place in Kant's practical philosophy; not as constituent facts about reality, but as regulative concepts that provide the basic assumptions or postulates of a highly powerful ethical theory.