From The Life And Times of Aodh O’Neill by John Mitchel. The letter has been rendered by the transcriber from archaic to modern English.

Those chiefs who still held back from the national confederacy, and could not be moved by persuasion, he treated as enemies, wasting their lands and pursuing them with fire and sword, – that so they might be brought to a better mind. One of the most powerful of these refractory lords was the Viscount Barry. O’Neill therefore let loose a body of troops upon his country, took some prisoners, and drove away a spoil of three thousand cows and four thousand horses; – and then, having given him so intelligible a warning, reasoned with him earnestly by letter: –

MY LORD BARRY. Your impiety to God, cruelty to your soul and body, tyranny and ingratitude both to your followers and country are inexcusable and intolerable. You separated yourself from the unity of Christ’s mystical body, the Catholic Church. You know the sword of extirpation hangeth over your head as well as ours, if things fall out other ways than well: you are the cause why all the nobility of the South (from the east part unto the west), you being linked unto each of them, either in affinity or consanguinity, are not linked together to shake off the cruel yoke of heresy and tyranny, with which our souls and bodies are oppressed. All those aforesaid, depending of your resolution, and relying to your judgment in this common cause of our religion and country; you might forsooth with their help, (and the rest that are combined in this holy action,) not only defend yourself from the incursion and invasion of the English, but also (by God’s assistance, who miraculously and above all expectation gave good success to the cause principally undertaken for his glory, exaltation of religion, next for the restoration of the ruins and preservation of the country,) expel them and deliver [them and] us from the most miserable and cruel exaction and subjection, enjoy your religion, safety of wife and children, life, lands, and goods, which all are in hazard through your folly. – Enter, I beseech you, into the closet of your conscience, and like a wise man weigh seriously the end of your actions, and take advice of those that can instruct you and inform you better than your own private judgment can lead you unto. Consider and read with attention and settled mind this discourse I send you; that it may please God to set open your eyes and grant you a better mind. From the camp this instant, Tuesday, the sixth of March, according to the new computation. I pray you to send me the papers I sent you as soon as your honour shall read the same.