We, moreover, proclaim, declare and pronounce that it is altogether necessary to salvation for every human being to be subject to the Roman Pontiff.

Source: Pope Boniface VIII, Bull Unam Sanctam, promulgated November 18, 1302, in Translations and Reprints From the Original Sources of European History, Vol. 3 (Philadelphia: University of Pennsylvania Press, 189–), No. 6, pp. 20–23 (from Latin text of Mury, Revue des Questions Historiques, Vol. 46, pp. 225, 256, based on the facsimile from the Papal Regesta).

Liberally minded Catholic apologists will sometimes suggest that Boniface VIII meant to apply his remark only to Catholics, and that Protestants are not automatically excluded from salvation by it. However the Latin text (in David S. Schaff, The Middle Ages [Philip Schaff, History of the Christian Church, Vol. 5. New York: Scribner, 1910], part 2, p. 28) reads omni humanae creaturae(“every human creature”). The title of the bull, Unam Sanctam (One Holy Church) and its last sentence make clear that Boniface VIII was declaring that submission to the Pope of the Holy See of Rome of the Catholic Church was the only means of salvation and that those resisting that presumed authority were lost souls. Conservative traditional Catholics will staunchly defend the statement that “Outside the Catholic Church there is no Salvation”, and will cite Unam Sanctam as proof positive.

Here is the full text of UNAM SANCTAM online.

The Decision of the Pope and the Decision of God Constitute One Decision.

Second reason considering the role of the Pope. Only the Pope is said to be the Vicar of God: because he alone is able to bind and loose, possessing alone loosing and binding given to him by God. The decision of the Pope and the decision of God constitute one decision, just as the decision of the Pope and his disciple are the same. Since, therefore, an appeal is always taken from an inferior judge to a superior, as no one is greater than himself, so no appeal holds when made from the Pope to God, because there is one consistory of the Pope himself and of God Himself, of which consistory the Pope himself is the key-bearer and the doorkeeper. Therefore no one can appeal from the Pope to God, as no one can enter into the consistory of God without the mediation of the Pope, who is the key-bearer and the doorkeeper of the consistory of eternal life; and as no one can appeal to himself, so no one can appeal from the Pope to God, because there is one decision and one court of God, and the Pope.

Summa de potestate ecclesiastica, Augustini Triumphi (Agostino Trionfo), Question 6 Ad 1. See 666, The Number of the Beast for details.

Also well known is the Catholic teaching that no one can be saved outside the Catholic Church. Eternal salvation cannot be obtained by those who oppose the authority and statements of the same Church and are stubbornly separated from the unity of the Church and also from the successor of Peter, the Roman Pontiff, to whom “the custody of the vineyard has been committed by the Savior.”

Source: QUANTO CONFICIAMUR MOERORE, On Promotion of False Doctrines, Encyclical of Pope Pius IX, August 10, 1863.

I alone, despite my unworthiness, am the successor of the apostles, the vicar of Jesus Christ: I alone have the mission to guide and direct the bark of Peter. I am the way, the truth, and the life: they who are with me are with the church: they who are not with me are out of the church—they are out of the way, the truth, and the life. Let men well understand this, that they be not deceived, or led astray by soi-disant Catholics, who desire and teach something quite different from what the head of the church teaches. (The Guardian, London, April 11, 1866)

Attributed to Pius IX, who on March 24, 1866, spoke in French, in response to an address by Catholics of various nations in which certain liberal ideas were expressed. Published in France in the Catholic monthly Revue du Monde Catholique, the L’ Union, and the Observateur Catholique of April 1, 1866, p. 357.