There is another evil besides that spirit of conformity with the world of which I have before told you, that religious persons may easily fall into. Catholics have, perhaps, much reason to be apprized of this. It may be, that by a strong and becoming zeal against the opinions (for their religion is too often little else than opinion) of those who are not of their own Church, they overlook their own great sinfulness, and even their own guiltiness before God. Two apostles, one of them the loving John, would have commanded fire from heaven upon those whom they deemed Christ's enemies. Jesus rebuked them, saying, you know not of what spirit you are. True piety is like a mighty, but gentle heat, which cherished in the heart disperses a warm, but calm and quiet spirit, through the members of the body, not inflaming any with hot and feverish impulses. Like Aaron's serpent, which eat up the serpents of the Egyptian magicians, true Christian piety absorbs and swallows up passions and prejudices, which self, and not the grace of God, stirs up in us; while our Lord said to the Samaritan woman: You adore that which you know not, we adore that which we know; for salvation is of the Jews, so far from showing any hot zeal against the Samaritans, he again and again makes them the subjects of His commendation and examples of virtue and grace to the Jews, His own people. That religion which runs out into vehemence against others, whether expressed by our unkind actions or sour words, or kept and even cherished within us, as a temper of our minds does not come from heaven: from that God who is love: The Lord is sweet to all, and his tender mercies are over all his works.
- text taken from Daily Bread - Bring a Few Morning Meditations for the Use of Catholic Christians by Father Richard Waldo Sibthorp