Kant defines God the Father as the author of the categorical imperative and understands Jesus Christ as its teacher on earth. Thus Jesus is the founder of the one true church, not because of his redemptive sacrifice on the cross, but because of his sermons, parables, and exemplary life as the perfect exponent of the moral law. This interpretation is expounded mainly in two sections of part 4 that consider Christianity first as a natural or pretheoretical religion, then as a learned or revealed religion.
Christianity as a Kantian natural religion is tantamount to belief in divinely sanctioned morality. It is spread and maintained by teachers rather than priests and informed by conscience rather than dogma. Its goal is unanimity of moral sentiment and universalizability of the derived maxims of moral action. Kant cites Matthew 5:20-48 to argue that the only people who please God are the morally pure. He uses Matthew 7:13-21 to show that those who act immorally cannot redeem themselves by doing good works for the church. For Kant, duty to the church is unimportant compared with duty to God.
At the more sophisticated stage of revealed religion, Christianity is characterized by theological principles interpreted through historical events such as the life of Jesus, the writing of the New Testament, and the growth of the church. Intellectuals working within the church create a learned faith that can appeal to all people. Faith is not an end in itself. Adherence to simple faith is not sufficient for salvation. The end for Kant is always morality. Kant calls even the most devout service to the church pseudoservice if it consists of obeying priests, believing dogma, or worshiping supernatural beings. True service to the church consists of following the good principle by doing one’s duty to the moral law, which Christian theology partially reveals and fully supports.
Kant also differentiates the earthly, historical, or visible church from the heavenly, universal, or invisible church. Both constitute what Kant calls an ethical commonwealth, but the former is temporal, essentially political, and therefore prone to all manner of civil conflict, while the latter is the perfectly harmonious eternal Kingdom of God. The mission of Jesus was to found the Kingdom of God on earth as an ethical commonwealth in which people would obey God’s moral law without fail, despite their evil nature.