Zeal for the salvation of souls is a sublime virtue, and yet how many errors and sins are committed daily in its name! Evil is never done more effectually and with greater security, says St. Francis de Sales, than when one does it believing he is working for the glory of God.
The saints themselves can be mistaken in this delicate matter. We see a proof of this in the incident related to the Apostles Saint James and Saint John; for Our Lord reprimanded them for asking Him to cause fire from heaven to fall upon the Samaritans. (Luke, IX., 54.)
Acts of zeal are like coins the stamp upon which is necessary to examine attentively, as there are more counterfeits than good ones. Zeal to be pure should be accompanied by great humility, for it is of all virtues the one which self-love most easily glides. When it does so, zeal is apt to become imprudent, presumptuous, unjust, bitter. Let us consider these characteristics in detail, viewing them, for the sake of greater clearness, in their practical bearings....
"If your zeal is bitter", says St. James, "it is not wisdom descending from on high, but earthly, sensual, diabolical". (James III, 14-15.) These words of an Apostle should furnish matter of reflection for those persons who, whilst making profession of piety, are so prone to irritability, so harsh and rude in their manner and language, that they might be taken for angels in church and for demons elsewhere.
The value and utility of zeal are in proportion to its tolerance and amiability. True zeal is the offspring of charity; it should then, resemble its mother and show itself like to her in all things. "Charity", says St. Paul, "is patient, is kind, is not ambitious, and seeks not her own." (1 Cor. XIII, 4-5.)...
Never allow your zeal to make you overeager to correct others, says [St. Francis de Sales]; and when you do it remember that the most important thing to consider is the choice of the moment. A caution deferred can be given another time: one given inopportunely is not only fruitless, but moreover paralyzes beforehand all the good that might have have subsequently been done.
Be zealous therefore, ardently zealous for the salvation of your neighbour, and to further make use of whatever means God has placed in your power; but do not exceed these limits nor disquiet yourself about the good you are unable to do, for God can accomplish it through others. In conclusion, zeal according to the teaching of the Fathers of the Church, should always have truth for its foundation, indulgence for its companion, mildness for its guide, prudence for its counsellor and director.
I've always found intemperate zeal a very strong temptation, and I think it is often such for orthodox Catholics. After all, we have the truth, and we see it being flagrantly ignored not only by 'the world' but also, it often seems, by the majority of our co-religionists. Nor are these disagreements merely over small matters (which hasn't stopped people from getting very, very ,very worked up over questions like communion rails and reception under both forms) but over moral issues of the very greatest gravity.
We live in a depraved world (all people, in all times have lived in pretty depraved worlds) and at times the temptation is great to simply shout: "Don't you freaks understand that half our children are born out of wedlock, the permanence of marriage has become a joke, porn is everywhere and we're killing over a million of our own children every year? What's wrong with you?"
And yet, much though all of this demands our outrage (As the bumper sticker says: If you're not outraged, you haven't been paying attention.) the 'freaks' are generally not going to listen to people calling them such.
Politeness and (to use the much abused word) ecumenism contain their own inherent temptations. We know all too many examples of people who have come to feel that the mere strength of an opinion or belief disqualifies it from being true. (Thus, all the demands that the pro-life movement 'calm down'.) Likewise, we know of people who take the step from respecting the beliefs of others to claiming that others (mutually contradictory) beliefs are in fact equally true, or at least "true for them".
Aristotle held that virtue is always found in the mean between the vices of two extremes. Certainly, in zeal this seems to be the case.