“What earlier generations held as sacred remains sacred and great for us too, and it cannot be all of a sudden entirely forbidden and even considered harmful.” 

—Pope Benedict XVI, Letter to the Bishops of the Catholic Church on the occasion of the publication of the motu proprio Summorum Pontificum, July 7, 2007.

“The Holy Spirit was not promised to the successor of Peter that by the revelation of the Holy Spirit they might disclose new doctrine, but that by His help they might guard sacredly the revelation transmitted through the Apostles and the deposit of faith, and might faithfully set it forth.”

—  First Vatican Council.

“For the Church of Christ, watchful guardian that she is, and defender of the dogmas deposited with her, never changes anything, never diminishes anything, never adds anything to them; but with all diligence she treats the ancient documents faithfully and wisely; if they really are of ancient origin and if the faith of the Fathers has transmitted them, she strives to investigate and explain them in such a way that the ancient dogmas of heavenly doctrine will be made evident and clear, but will retain their full, integral, and proper nature, and will grow only within their own genus – that is, within the same dogma, in the same sense and the same meaning.”

—Pope Pius IX, “Ineffabilis Deus”, 1854 A.D. Emphasis added.

“If anyone says that it is possible that at some time, given the advancement of knowledge, a sense may be assigned to the dogmas propounded by the Church which is different from that which the Church has understood and understands: let him be anathema.” 

— First Vatican Council.

“I entirely reject the heretical misrepresentation that dogmas evolve and change from one meaning to another different from the one which the Church held previously.”

— From the Oath Against Modernism, Prescribed by Pope St. Pius X, 1910 A.D.

“Christ is the teacher and the exemplar of all sanctity, and to His standard must all those conform who wish for eternal life. Nor does Christ know any change as the ages pass, ‘for He is yesterday and today and the same forever. (Hebrews xiii, 8)”

— Pope Leo XIII, “Testem Benevolentiae Nostrae”, 1899 A.D.

 “One should not seek among others the truth that can be easily gotten from the Church. For in her, as in a rich treasury, the apostles have placed all that pertains to truth, so that everyone can drink this beverage of life. She is the door of life.” 

–-St. Irenaeus of Lyons c. 130-c. 202 A.D.

“Let what you heard from the beginning remain in you. If what you heard from the beginning remains in you, then you will remain in the Son and in the Father. And this is the promise that he made us: eternal life. I write you these things about those who would deceive you.”

— St. John, 1 Jn. 2:24-26

See The Credo of the People of God

Progressivist Theology: What it is.