The study examines the noumenal, the spiritual essence of religion. Starting from Kant's practical philosophy, it shows that this noumenon, which is seen as the indirect symbolic way of understanding the world, is familiar to everybody who strives to lead a good and honest life, including those with an atheistic orientation. The author accesses the normative critical concept of religion in three stages. To start with, central aporias of Kant's practical philosophy (doctrine of postulates, theory of the highest good) are reconstructed and cancelled using the synthetic practical proposition a priori. In the second stage, these aporias are related to further topics of Kant's practical philosophy in order to elucidate the importance of religion for practical consciousness. In the third section, the concept of religion gained systematically is further developed to a critical normative concept of phenomenal religion. With this concretisation the noumenal religion becomes a generalized concrete concept when compared with a mere rational religion.