- If Protestant theology has reached the point where it is closed to the challenge of atheism, then it has ceased to be the intellectual vanguard of Christianity.
- Thomas J. J. Altizer, Toward a New Christianity (1967), p. 7
- The Christian ecumenical movement will have reached its limit, meaning that Catholicism will have turned into Protestantism and Protestantism into agnosticism....But Islam will not have lost any of its rigour....Supernature abhors a supervacuum. With the death of institutional Christianity will come the spread of Islam.
- All protestantism, even the most cold and passive, is a sort of dissent. But the religion most prevalent in our northern colonies is a refinement on the principles of resistance: it is the dissidence of dissent, and the protestantism of the Protestant religion.
- Although the Protestant Church is accused of much disastrous bigotry, one claim to immortal fame must be granted it: by permitting freedom of inquiry in the Christian faith and by liberating the minds of men from the yoke of authority, it enabled freedom of inquiry in general to take root in Germany, and made it possible for science to develop independently. German philosophy, though it now puts itself on an equal basis with the Protestant Church or even above it, is nonetheless only its daughter; as such it always owes the mother a forbearing reverence.
- Heinrich Heine, “The Romantic School,” The Romantic School and Other Essays, J. Hermand, ed. (1985), P. 24
- Protestantism itself, in its early phases, was plainly a movement toward mysticism: its purpose, at least in theory, was to remove the priestly veil separating man from the revealed Word of God. But that veil was restored almost instantly, and by the year 1522, five years after Wittenberg, Luther was damning the Anabaptists with all the ferocious certainty of a medieval Pope, and his followers were docily accepting his teaching.
- In Catholic doctrine, divine revelation did not end with the scriptures, but continued from age to age through the medium of the Church... Protestants, on the contrary, rejected the Church as a vehicle of revelation; truth was to be sought only in the Bible, which each man could interpret for himself. ...In practice, the State claimed the right that had formerly belonged to the Church, but this was a usurpation. In Protestant theory, there should be no earthly intermediary between the soul and God.
- Any of several church denominations denying the universal authority of the Pope and affirming the Reformation principles of justification by faith in Jesus alone, the priesthood of all believers, and the primacy of the Bible as the only source of revealed truth" and, more broadly, to mean Christianity outside "of an Orthodox or Catholic church"
- Merriam Webster.com. "Protestantism" on merriam-webster.com dictionary
- For what is specific in the Catholic religion is immortalization and not justification, in the Protestant sense. Rather is this latter ethical. It is from Kant, in spite of what orthodox Protestants may think of him, that Protestantism derived its penultimate conclusions — namely, that religion rests upon morality, and not morality upon religion, as in Catholicism.
- Miguel de Unamuno The Tragic Sense of Life (1913) IV : The Essence of Catholicism