Without denying the importance of a range of independent epistemic and metaphysical considerations, I argue that there is an irreducibly theological dimension to the emergence of Kant's transcendental idealism. Creative tasks carried out by the divine mind in the pre-critical works become assigned to the human noumenal mind, which is conceived of as the (created) source of space, time and causation. Kant makes this shift in order to protect the possibility of transcendental freedom. I show that Kant has significant theological difficulties ascribing such transcendental freedom to creatures in relation to God, and that he intends transcendental idealism to be a solution to these difficulties. I explain how this provides Kant with a powerful motivation and reason for denying the so-called “neglected alternative”, and conclude by suggesting that the nature of any theological response to Kant will depend upon some fundamental options about how to conceive of the relationship between the creator and creation.