If your right eye causes you to sin, tear it out and throw it away. It is better for you to lose one of your members than to have your whole body thrown into Gehenna. And if your right hand causes you to sin, cut it off and throw it away. It is better for you to lose one of your members than to have your whole body go into Gehenna (Mt 5:30)

Then Jesus approached and said to them, ‘All power in heaven and on earth has been given to me. Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the holy Spirit, teaching them to observe all that I have commanded you.’ (Mt 28:18-20)

I wrote you in my letter not to associate with immoral people, not at all referring to the immoral of this world or the greedy and robbers or idolaters; for you would then have to leave the world. But I now write to you not to associate with anyone named a brother, if he is immoral, greedy, an idolater, a slanderer, a drunkard, or a robber, not even to eat with such a person. For why should I be judging outsiders? Is it not your business to judge those within? God will judge those outside. ‘Purge the evil person from your midst.’ (1Cor 5:9-13)

Anyone who is so ‘progressive’ as not to remain in the teaching of the Christ does not have God; whoever remains in the teaching has the Father and the Son. If anyone comes to you and does not bring this doctrine, do not receive him in your house or even greet him; for whoever greets him shares in his evil works. (2Jn 9-11)

Today, having a clear faith based on the Creed of the Church is often labeled as fundamentalism. Whereas relativism, that is, letting oneself be ‘tossed here and there, carried about by every wind of doctrine’, seems the only attitude that can cope with modern times. We are building a dictatorship of relativism that does not recognize anything as definitive and whose ultimate goal consists solely of one’s own ego and desires. We, however, have a different goal: the Son of God, the true man. He is the measure of true humanism. An ‘adult’ faith is not a faith that follows the trends of fashion and the latest novelty… (Cardinal Joseph Ratzinger. Homily at Pro eligendo Romano Pontifice Mass, April 18, 2005)

To what extent should the Church adapt itself to the historical and local circumstances in which it has to exercise its mission? How is it to guard against the danger of relativism which would make it untrue to its own dogmas and moral principles? And yet how can it fit itself to approach all men and bring salvation to all, becoming on the example of the Apostle Paul ‘all things to all men,’ that all may be saved? (1Cor 9: 22). […] But the danger remains. Indeed, the worker in the apostolate is under constant fire. The desire to come together as brothers must not lead to a watering down or whittling away of truth. Our dialogue must not weaken our attachment to our faith. Our apostolate must not make vague compromises concerning the principles which regulate and govern the profession of the Christian faith both in theory and in practice. An immoderate desire to make peace and sink differences at all costs (irenism and syncretism) is ultimately nothing more than skepticism about the power and content of the Word of God which we desire to preach. The effective apostle is the man who is completely faithful to Christ’s teaching. He alone can remain unaffected by the errors of the world around him, the man who lives his Christian life to the full. (Paul VI. Encyclical Ecclesiam suam, August 6, 1964)

Obviously we cannot agree with these various forms of religion, nor can we adopt an indifferent or uncritical attitude toward them on the assumption that they are all to be regarded as on an equal footing, and that there is no need for those who profess them to enquire whether or not God has Himself revealed definitively and infallibly how He wishes to be known, loved, and served. Indeed, honesty compels us to declare openly our conviction that the Christian religion is the one and only true religion, and it is our hope that it will be acknowledged as such by all who look for God and worship Him. (Paul VI. Encyclical Ecclesiam suam, August 6, 1964)

We are firmly convinced that the basic propositions of atheism are utterly false and irreconcilable […] We shall therefore resist this growing evil with all our strength, spurred on by our great zeal for safeguarding the truth, inspired by our social duty of loyally professing Christ and His gospel, and driven on by a burning, unquenchable love, which makes man’s good our constant concern. We shall resist in the invincible hope that modern man may recognize the religious ideals which the Catholic faith sets before him and feel himself drawn to seek a form of civilization which will never fail him but will lead on to the natural and supernatural perfection of the human spirit. (Paul VI. Encyclical Ecclesiam suam, August 6, 1964)

For the Church, evangelizing means bringing the Good News into all the strata of humanity, and through its influence transforming humanity from within and making it new: ‘Now I am making the whole of creation new’ (Rev 21:5). But there is no new humanity if there are not first of all new persons renewed by Baptism and by lives lived according to the Gospel. The purpose of evangelization is therefore precisely this interior change, and if it had to be expressed in one sentence the best way of stating it would be to say that the Church evangelizes when she seeks to convert, solely through the divine power of the message she proclaims, both the personal and collective consciences of people, the activities in which they engage, and the lives and concrete milieu which are theirs. (Paul VI. Apostolic Exhortation Evangelii nuntiandi, no. 18, December 18, 1975)

Strata of humanity which are transformed: for the Church it is a question not only of preaching the Gospel in ever wider geographic areas or to ever greater numbers of people, but also of affecting and as it were upsetting, through the power of the Gospel, mankind’s criteria of judgment, determining values, points of interest, lines of thought, sources of inspiration and models of life, which are in contrast with the Word of God and the plan of salvation. (Paul VI. Apostolic Exhortation Evangelii nuntiandi, no. 19, December 18, 1975)

For, to reject the supreme authority to God, and to cast off all obedience to Him in public matters, or even in private and domestic affairs, is the greatest perversion of liberty and the worst kind of liberalism; and what We have said must be understood to apply to this alone in its fullest sense. (Leo XIII. Encyclical Libertas praestantissimum, no. 37, June 20, 1888)

Now we examine another prolific cause of evils by which, we lament, the Church is at present afflicted, namely indifferentism, or that base opinion which has become prevalent everywhere through the deceit of wicked men, that eternal salvation of the soul can be acquired by any profession of faith whatsoever, if morals are conformed to the standard of the just and the honest. . . . And so from this most rotten source of indifferentism flows that absurd and erroneous opinion, or rather insanity, that liberty of conscience must be claimed and defended for anyone. (Denzinger-Hünermann 2730. Gregory XVI, Encyclical Mirari vos, August 15, 1832)

In these times of confusion and disorder, it is not unusual to see Christians, Catholics – even within the secular clergy and cloisters – who constantly have a word of conformity, of conciliation and negotiation on their lips. Very well! I do not hesitate to declare: these men are in error, and do not consider them to be the lesser enemies of the Church. We live in a corrupt and pestilent atmosphere and we must know how to preserve ourselves from it. Let us not allow ourselves to be contaminated by false doctrines, which lose all things under the pretext of saving all. (Pius IX. Speech in the Church of Aracoeli, September 17, 1861)

Reading the Acts of the Apostles helps us to realize that at the beginning of the Church the mission ad gentes, while it had missionaries dedicated ‘for life’ by a special vocation, was in fact considered the normal outcome of Christian living, to which every believer was committed through the witness of personal conduct and through explicit proclamation whenever possible. (John Paul II. Encyclical Redemptoris missio, no. 27, December 7, 1990)