Why did Karl Jaspers believe philosophy should not become a substitute for religion?

Karl Jaspers sought to develop a philosophy that remained independent of science while ensuring it did not function as a substitute for religious belief.1

His approach was rooted in the belief that the primary task of philosophy is to appeal to the freedom of the individual as a subject who thinks and exists, focusing on human existence as the center of all reality. By maintaining this distinction, Jaspers aimed to avoid conflating philosophical inquiry with the specific dogmas or institutional structures of religion. Instead, he viewed philosophy as a subjective interpretation of Being that illuminates the totality of human existence—which he defined as the potentiality to realize one's freedom—rather than providing a set of religious norms or prophetic visions.1

While Jaspers later emphasized the religious character of faith in transcendence, he maintained that philosophy serves to read the "ciphers" of transcendence in history, nature, and human experience, rather than replacing the unique role of faith in one's life.23