Kant does not criticize all aspects of organized religion, but he does find many tensions between moral principles and religious traditions. There are many religions, all of them influenced by their historical period, but according to Kant there is one universal moral law. Furthermore, humans can determine that moral law by relying on their own instincts. They do not need organized religion to explain it to them. Kant also believes that religious practices often conflict with or undermine moral principles. He thinks that community life, even religious community life, can foster ugly impulses toward revenge and competition. Kant believes that religious institutions often identify religious experience with the performance of certain rituals or with the acceptance of certain beliefs. This is dangerous, because individuals can simultaneously adhere to the strictest requirements of a particular church, and nurse hatred or jealousy or immoral urges. Secondly, some religious traditions promote the idea that incantations or professions of faith endear people to God. The danger here is that people will behave morally not because it is the right thing to do, but because it is a daily chore designed to appease God. Finally, Kant objects to those religious traditions that say God's grace will save you, not your own good behavior. According to Kant, our actions have true moral worth only if we performed them independently, without God's assistance.
Kant is famous for his skeptical view of human nature. In some passages he seems to suggest that human nature is unqualifiedly evil, and that only a daily regimen of moral deliberation can quash our natural badness. In others he says that along with our inclination toward evil, we all possess a germ of good. He believes that humans can be either good or evil, not both at once. We use general rules called maxims to make decisions; all actions not based on maxims are simply responses to impulses and desires. This tendency to make decisions without thinking of our maxims is one of the signs of our evil natures. Kant calls it the frailty of human nature.
In addition to falling short of our ideals, our good behavior sometimes stems from selfish considerations. We do not always undertake the moral action for its own sake, but because the moral action also happens to save us money, or win us attention, or benefit us in some unseemly way. This tendency to augment a sense of duty with immoral incentives is the second variety of our inclination to evil, which Kant calls the impurity of human nature.
There is a third variety of the inclination. Kant calls it the depravity of human nature. Depraved people consciously allow immoral incentives to drive their behavior.
Kant says the struggle between good and evil is a struggle between moral principles and immoral incentives. In order to be good, we must consciously develop a virtuous disposition and also combat our tendency to engage in evil. As Kant puts it in the very beginning of Part Two: "To become a morally good human being is not enough to let the germ of the good which lies in our species develop unhindered; there is in us an active and opposing cause of evil which must also be combated." If the good is nurtured and the evil ignored, the evil will flourish.
To actively develop our moral tendencies and combat our evil ones, we need a model of truly moral behavior. According to Kant, the most compelling historical modal of moral behavior is Jesus of Nazareth, for he is said to have resisted all temptations. Kant says that it is not necessary to believe that Jesus was the son of God, but it is important to believe in the possibility that Jesus actually attained moral perfection. If one human could be perfect, we could be perfect, too. We must also realize that a total change of heart is necessary to become morally good. Even if the tendency to evil can never be eradicated completely, our commitment to the moral law must be sincere and wholehearted.
Kant says that a virtuous society must emerge if moral behavior is to become common. Such a virtuous society would recognize the difference between coercive political laws, such as speed limits and anti-loitering statutes, and unenforceable ethical laws. Ethical laws are private and impossible to enforce, but the ideal society would promote them. Kant thinks the best way to promote ethical laws is through the "church invisible." This church does not exist in the traditional sense; it is an ideal that actual churches should strive to emulate.
The invisible church exists to ensure that people will find the moral law accessible, relatively easy to understand, and relevant to their daily lives. The invisible church is universal; it applies equally to everyone. It is pure, promoting only that behavior that accords with the moral law. Its members freely accept the moral law rather than having it forced upon them. Finally, there is a morally acceptable hierarchy among its members.