‘And today we again repeat with all the insistency We can command: it is not enough to be a member of the Church of Christ, one needs to be a living member, in spirit and in truth, i.e., living in the state of grace and in the presence of God, either in innocence or in sincere repentance. If the Apostle of the nations, the vase of election, chastised his body and brought it into subjection: lest perhaps, when he had preached to others, he himself should become a castaway (1 Cor. ix. 27), could anybody responsible for the extension of the Kingdom of God claim any other method but personal sanctification? Only thus can we show to the present generation, and to the critics of the Church that “the salt of the earth,” the leaven of Christianity has not decayed, but is ready to give the men of today – prisoners of doubt and error, victims of indifference, tired of their Faith and straying from God – the spiritual renewal they so much need. A Christianity which keeps a grip on itself, refuses every compromise with the world, takes the commands of God and the Church seriously, preserves its love of God and of men in all its freshness, such a Christianity can be, and will be, a model and a guide to a world which is sick to death and clamors for directions, unless it be condemned to a catastrophe that would baffle the imagination.
‘Every true and lasting reform has ultimately sprung from the sanctity of men who were driven by the love of God and of men. Generous, ready to stand to attention to any call from God, yet confident in themselves because confident in their vocation, they grew to the size of beacons and reformers. On the other hand, any reformatory zeal, which instead of springing from personal purity, flashes out of passion, has produced unrest instead of light, destruction instead of construction, and more than once set up evils worse than those it was out to remedy. No doubt “the Spirit breatheth where he will” (John iii. 8): “of stones He is able to raise men to prepare the way to his designs” (Matt. iii. 9). He chooses the instruments of His will according to His own plans, not those of men. But the Founder of the Church, who breathed her into existence at Pentecost, cannot disown the foundations as He laid them. Whoever is moved by the spirit of God, spontaneously adopts both outwardly and inwardly, the true attitude toward the Church, this sacred fruit from the tree of the cross, this gift from the Spirit of God, bestowed on Pentecost day to an erratic world.’
– Pope Pius XI, Mit Brennender Sorge, On The Church and the German Reich, n.19-20, published 1937
I recommend reading the whole encyclical. It’s fascinating historically, but it also contains a number of remarkably relevant passages for our own times and circumstances.