the privatization of religion

The idea that religion is a matter of pure faith is a distinctly Protestant idea. Luther held it and Kant, the philosopher of Protestantism, held it too. This is an idea foreign to the Catholic tradition which holds that reason and faith are complementary human abilities to reach God.

A Protestant society could not survive, much less prosper, with multiple religious sects competing in the public domain, each one of them claiming to have the truth over the others. This was a source of civil turmoil and ultimately of civil war. Leaving the idea of God outside the field of pure reason, Kant took religion out of the public domain of society and made it a private affair.

Soon Nietzsche, following in Kant's steps, would proclaim the death of God. This was true in the public domain of society as God was indeed banned from public speech. Kant himself at one point was reprimanded by the emperor for writing about religious issues and he refrained from doing so for the next several years.

The privatization of religion was a necessity in Protestant societies, an essential condition for civil peace, and Kant provided the rationale for it. From then on religion became a private competitive activity in Protestant societies whereas in Catholic countries it remained a public monopoly of the Catholic Church.