As previously indicated part of Kant's initial mission, or so it appears, was to establish a firm foundation for theological and metaphysical speculation about the cosmos.
Unfortunately in the end Kant was forced to face the fact that such a foundation was impossible to establish due to the limitations of our ability to "know" since knowledge of things such as "God" and "the soul" is not conducive to the human epistemologic apparatus.
Kant eventually determined that it is impossible for us to know that God existed. However, Kant still believed in some fashion in the existence of "God" and he realized that such belief was a matter of faith and therefore not actually knowable. Knowledge of God belongs to a "Transcendental" realm.
Closely related to the issue of believing in the existence of God, Kant based this belief upon his conclusions regarding morality. Kant concluded that there is a sense of morality or a sense of oughtness present within each individual. At this point Kant turned things upside down.
Kant's predecessors had argued from God to morality. They had assumed that moral convictions and religious convictions stand in need of a metaphysical foundation. They started with God and reasoned their way forward to morality.
However Kant reversed the process. He argued that the presence of a sense of oughtness or the presence of this sense of morality lead us inevitably to speculation about the metaphysical doctrine about God.
In other words, Kant's predecessors started with God and moved to morality. But Kant starts with morality and its universality, its being "built in" us and he thereby deduced the existence of the God who put it there.
