Tu es Petrus (Grad., Missa in Festo SS. Ap. Petri et Pauli)
Kingdoms and empires have passed away; peoples once renowned for their history and civilization have disappeared; time and again the nations, as though overwhelmed by the weight of years, have fallen asunder; while the Church, indefectible in her essence, united by ties indissoluble with her heavenly Spouse, is here today radiant with eternal youth, strong with the same primitive vigor with which she came from the Heart of Christ dead upon the Cross. Men powerful in the world have risen up against her. They have disappeared, and she remains. Philosophical systems without number, of every form and every kind, rose up against her, arrogantly vaunting themselves her masters, as though they had at last destroyed the doctrine of the Church, refuted the dogmas of her faith, proved the absurdity of her teachings. But those systems, one after another, have passed into books of history, forgotten, bankrupt; while from the Rock of Peter the light of truth shines forth as brilliantly as on the day when Jesus first kindled it on His appearance in the world, and fed it with His Divine words: "Heaven and earth shall pass, but my words shall not pass" (Matth. xxiv. 35).
We, strengthened by this faith, firmly established on this rock, realizing to the full all the heavy duties that the Primacy imposes on Us - but also all the vigor that comes to Us from the Divine Will - calmly wait until all the voices be scattered to the winds that now shout around Us proclaiming that the Church has gone beyond her time, that her doctrines are passed away for ever, that the day is at hand when she will be condemned either to accept the tenets of a godless science and civilization or to disappear from human society. Yet at the same time We cannot but remind all, great and small, as Pope St. Gregory did, of the absolute necessity of having recourse to this Church in order to have eternal salvation, to follow the right road of reason, to feed on the truth, to obtain peace and even happiness in this life.
Pope Saint Pius X