Complex sentence: To insulate theology from reductionism, 19th century post-Enlightenment German theologians, especially Friedrich Schleiermacher and Albrecht Ritschl, used the Romantic method of basing religion on the human spirit, so that it is a person's feeling or sensibility about spiritual matters that comprises religion.
Split into simpler sentences: To insulate theology from reductionism, 19th century post-Enlightenment German theologians moved in a new direction, led by Friedrich Schleiermacher and Albrecht Ritschl. They took the Romantic approach of rooting religion in the inner world of the human spirit, so that it is a person's feeling or sensibility about spiritual matters that comprises religion.