1 Corinthians 12:26
Wherefore I beseech you, leaving this evil way, to change to a proper emulation, (for it is a violent thing, this kind of zeal, and hotter than any fire,) and to win thereby mighty blessings. Thus also Paul used to guide those of Jewish origin unto the faith, saying, “If by any means I may provoke to emulation them which are my flesh, and may save some of them.” For he whose emulation is like what Paul wished for does not pine when he sees the other in reputation, but when he sees himself left behind: the envious not so, but at the sight of another's prosperity. And he is a kind of drone, injuring other men's labors; and himself never anxious to rise, but weeping when he sees another rising, and doing every thing to throw him down. To what then might one compare this passion? It seems to me to be like as if a sluggish ass and heavy with abundance of flesh, being yoked with a winged courser, should neither himself be willing to rise, and should attempt to drag the other down by the weight of his carcass. For so this man takes no thought nor anxiety to be himself rid of this deep slumber, but does every thing to supplant and throw down him that is flying towards heaven, becoming an exact emulator of the devil: since he too, seeing man in paradise, sought not to change his own condition, but to cast him out of paradise. And again, seeing him seated in heaven and the rest hastening there, he holds to the same plan, supplanting them who are hastening there and hereby heaping up the furnace more abundantly for himself. For in every instance this happens: both he that is envied, if he be vigilant, becoming more eminent; and he that is envious, accumulating to himself more evils. Thus also Joseph became eminent, thus Aaron the priest: the conspiracy of the envious caused God once and again to give His suffrage for him, and was the occasion of the rod's budding. Thus Jacob attained his abundant wealth and all those other blessings. Thus the envious pierce themselves through with ten thousand evils. Knowing as we do all these things, let us flee such emulation. For wherefore, tell me, do you envy? Because your brother has received spiritual grace? And from whom did he receive it? Answer me. Was it not from God? Clearly then He is the object of the enmity to Which you are committing yourself, He the bestower of the gift. Do you see which way the evil is tending, and with what sort of a point it is crowning the heap of your sins; and how deep the pit of vengeance which it is digging for you?
Let us flee it, then, beloved, and neither envy others, nor fail to pray for our enviers and do all we can to extinguish their passion: neither let us feel as the unthinking do who being minded to exact punishment of them, do all in their power to light up their flame. But let not us do so; rather let us weep for them and lament. For they are the injured persons, having continual worm gnawing through their heart, and collecting a fountain of poison more bitter than any gall. Come now, let us beseech the merciful God, both to change their state of feeling and that we may never fall into that disease: since heaven is indeed inaccessible to him that has this wasting sore, and before heaven too, even this present life is not worth living in. For not so thoroughly are timber and wool wont to be eaten through by moth and worm abiding therein, as does the fever of envy devour the very bones of the envious and destroy all self-command in their soul.
In order then that we may deliver both ourselves and others from these innumerable woes, let us expel from within us this evil fever, this that is more grievous than any gangrene: that having regained spiritual strength, we may both finish the present course and obtain the future crowns; unto which may we all attain, by the grace and mercy of our Lord Jesus Christ, with Whom to the Father, with the Holy Ghost, be glory, power, honor, now and ever, and world without end. Amen.
Source: Homilies on First Corinthians (New Advent)