Rorate Caeli

The dangers of uncontrolled zeal and of false zeal

Now as [Mathathias] left off speaking these words, there came a certain Jew in the sight of all to sacrifice to the idols upon the altar in the city of Modin, according to the king's commandment. And Mathathias saw and was grieved, and his reins trembled, and his wrath was kindled according to the judgment of the law, and running upon him he slew him upon the altar: Moreover the man whom king Antiochus had sent, who compelled them to sacrifice, he slew at the same time, and pulled down the altar. And shewed zeal for the law ... . [Roman Breviary, from the Second Lesson for Wednesday in the Fist Week in October, I Mac. ii, 23-26.]
It is true, indeed, my friend Theotimus, that Moses, Phinees, Elias, Mathathias and many great servants of God made use of anger in the exercise of their zeal, on many remarkable occasions, yet note also, I pray you, that those were great souls, who could well handle their passions and regulate their anger; like that brave captain of the Gospel who said to his soldiers: go, and they went, come, and they came: but we, who are, all of us, but common little people, have no such power over our movements; our horse is not so well broken in, that we can make him gallop or stop at our pleasure. Wise and well trained hounds run afield or come back according to the huntsman's call, but untrained young hounds break away and are disobedient. Great saints who have made their passions tractable, mortifying them by the exercise of virtue, can also turn about their anger as they like, send it out and draw it back as seems good to them; but we, who have unbridled passions, quite young, or at least mistaught, cannot let our anger go save at peril of great disorder, for being once loose we can no longer restrain or regulate it. 
...

S. Thomas Aquinas, that great star of theology, being sick of the disease of which he died, at the Monastery of Fossanuova, of the order of Citeaux, the religious besought him to make them a short exposition of the Canticle of Canticles in imitation of S. Bernard, and he answered them: "My dear fathers, give me S. Bernard's spirit and I will interpret this divine Canticle like S. Bernard." So verily, if it were said to one of us petty, miserable, imperfect and wretched Christians: use anger and indignation in your zeal, as did Phinees, Elias, Mathathias, S. Peter and S. Paul: we ought to reply: give us the spirit of perfection and pure zeal, with the interior light which those great saints had, and we will arm ourselves with anger as they did. It is not the fortune of every one to know how to be angry when and as he ought.

Those great saints were immediately inspired by God, and therefore might boldly employ their anger without peril; for the same Spirit which animated them to these great acts also held the reins of their just wrath lest they might transgress the prescribed bounds. Anger which is inspired or excited by the Holy Ghost is no longer the anger of man, and it is man's wrath that we are to beware of, because, as S. James says: The anger of man worketh not the justice of God. And indeed, when those great servants of God made use of anger, it was on occurrences so solemn and for crimes so excessive, that there was no danger that the punishment would exceed the fault.

... 
Zeal may be practised in three ways. First in performing great actions of justice to repel evil; and this belongs only to those who have the public offices of correcting, censuring, and reprehending in quality of superiors, such as princes, prelates, magistrates, preachers: but since this office is honourable, every one undertakes it, every one will have to do with it. Secondly, one may use zeal by doing actions of great virtue in order to give good example, by suggesting remedies for evils, and exhorting men to apply them, by effecting the good that is opposite to the evil which we desire to banish. This belongs to every one, and yet few will to do it. Finally, the most excellent use of zeal lies in suffering and enduring much to hinder or divert evil, and scarce any will have this sort of zeal. A specious zeal is all our ambition; upon that, each one willingly spends his talent, never attending to the fact that it is not zeal indeed which is thereby sought but glory, the satisfaction of our pride, anger, annoyance and other passions.

...
"O how happy is he," says S. Ambrose, who knows how to discipline zeal!" "The devil will easily," says S. Bernard, "delude thy zeal, if thou neglect knowledge; therefore let thy zeal be inflamed with charity, adorned with knowledge, established in constancy." True zeal is the child of charity as being its ardour; wherefore, like to charity, it is patient, is kind, envieth not, dealeth not perversely, seeketh not her own, is not provoked to anger, rejoiceth in the truth. The ardour of true zeal resembles that of the huntsman, being diligent, careful, active, industrious, eager in pursuit, but without passion, anger or disquiet, for if the huntsman's work were done in anger, bad temper and vexation, it would not be so much loved and desired. Zeal in like manner has ardours which are extreme, but constant, solid, sweet, industrious, equally agreeable and untiring; whereas on the contrary, false zeal is turbulent, troubled, insolent, arrogant, choleric, transient, equally impetuous and inconstant.
Saint Francis de Sales
Treatise on the Love of God