Martin Luther argued that because the Catholic Church had "lost sight of the doctrine of grace", it had "lost its claim to be considered as the authentic Christian church". This argument was open to the counter-criticism from Catholics that he was thus guilty of schism and the heresy of Donatism, and in both cases therefore opposing central teachings of the early Church and most especially the Church father St. Augustine of Hippo.[16] It also challenged the Catholic doctrine that the Catholic Church was indefectible and infallible in its dogmatic teachings.