According to James C. Livingston, "In the second Critique Kant sought to show that our relation to the world is not limited to scientific knowledge (fact), for the world is a stage upon which we must act -a realm of moral valuation." (Modern Christian Thought, Livingston, pg. 62) Thus, Kant set out to show that religion is not grounded in pure reason, but in what he called practical reason. Practical reason does not tell us facts about the world, but how to live. We execute, for Kant, practical reason when we try to understand our moral and religious situation; that is how to act.
In the second Critique, Kant postulates that everyone is under moral obligations, and that these moral obligations taken on various forms, thus are different for everyone. However, what is not different is that we all experience a sense of duty to act in a way which can become a universal maxim. Kant then takes morality to be a given, and as an a priori category, it can be used to ground all aspects of human life, even including religion.
Kant holds that morality is not something that is imposed from without, but comes from within. Morality is inherent in humanity. Therefore, morality, for Kant, cannot come from the Church or from Scriptures. Morality is prior to outside instruction for Kant. Now what does this mean for religion if morality is prior?
Like Rousseau before him, Kant holds that religion is grounded in morality. For Kant, "the only way to knowledge of God is through the moral conscience; the only genuine theology is moral theology." (pg. 63) Thus, as for Rousseau, speculative theology is not valid. As shown in the previous post, we cannot understand God and his attributes through Pure Reason. Thus, religion is only being moral.
By holding to this position, Kant is at the same time going counter the Eighteenth Century mentality and keeping it. He is going against the Eighteenth Century mentality by dismissing Reason as having any insight into Religion. He is keeping an Enlightenment view when he holds that morality is religion.
What does Kant's view then mean for the Church? "For Kant worshiping God was synonymous with obeying the moral law, and 'everything which, apart from a moral way of life, man believes himself of doing to please God' was for Kant 'mere religious delusion'". (pg. 64) The extra moral acts, such as all of the sacraments and attending Church for reasons other than moral instruction, are then for Kant worthless. And we see this mentality in the Church today, where the sacraments are either underplayed or non-existent and only morality is seen as true worship.