Cyprian of Carthage, On the Unity of the Church 3
My dearest brothers, we must guard ourselves not only against open and obvious dangers but also against those that deceive through the subtle cunning of fraud. For what could be more cunning, what more subtle, than this: the enemy, exposed and overthrown by the coming of Christ, saw the light come to the Gentiles and the saving light shine forth for the salvation of humankind, so that the deaf might receive the hearing of spiritual grace, the blind might open their eyes to God, the weak might recover strength through eternal health, the lame might run to the Church, and the mute might pray with clear voices and prayers; he saw idols abandoned and his own seats and temples deserted because of the great multitude of believers—and so he devised a new fraud, that under the very title of the Christian name he might deceive the unsuspecting? He has invented heresies and schisms by which he might subvert the faith, corrupt the truth, and tear apart unity. Those whom he cannot hold in the blindness of the old way, he encircles and deceives by the error of a new way. He snatches men from the Church itself; and while they appear to have drawn near to the light and escaped the darkness of the world, he pours fresh darkness into them unawares, so that, though they do not stand with the Gospel of Christ and with its observance and law, they call themselves Christians, and, walking in darkness, they think they possess the light—while the adversary flatters and deceives, transforming himself into an angel of light and his ministers into ministers of righteousness, as the Apostle says (2 Corinthians 11:14-15), declaring night to be day, destruction to be salvation, despair under the guise of hope, perfidy under the guise of faith, antichrist under the name of Christ; so that, while they utter plausible lies, they defeat the truth by subtlety. This happens, my dearest brothers, because we do not return to the origin of truth, nor seek the head, nor preserve the doctrine of the heavenly Master.
Latin
Cavenda sunt autem, fratres dilectissimi, non solum quae sunt aperta atque manifesta, sed et astutae fraudis subtilitate fallentia. Quid vero astutius, quidve subtilius, quam ut Christi adventu detectus ac prostratus inimicus, postquam lux Gentibus venit et sospitandis hominibus salutare lumen effulsit, ut surdi auditum gratiae spiritalis admitterent, aperirent ad Deum oculos suos caeci, infirmi aeterna sanitate revalescerent, claudi ad Ecclesiam currerent, muti claris vocibus et precibus orarent, videns ille idola derelicta et per nimium credentium populum sedes suas ac templa deserta, excogitaverit novam fraudem, ut sub ipso christiani nominis titulo fallat incautos? Haereses invenit et schismata, quibus subverteret fidem, veritatem corrumperet, scinderet unitatem. Quos detinere non potest in viae veteris caecitate, circumscribit et decipit novi itineris errore. Rapit de ipsa Ecclesia homines; et, dum sibi appropinquasse jam lumini atque evasisse saeculi noctem videntur, alias nescientibus tenebras rursus infundit, ut cum Evangelio Christi et cum observatione ejus et lege non stantes, Christianos se vocent, et ambulantes in tenebris habere se lumen existiment, blandiente adversario atque fallente, qui, secundum Apostoli vocem, transfigurat se velut angelum lucis, et ministros suos subornat velut ministros justitiae, asserentes noctem pro die, interitum pro salute, desperationem sub obtentu spei, perfidiam sub praetextu fidei, antichristum sub vocabulo Christi; ut, dum verisimilia mentiuntur, veritatem subtilitate frustrentur. Hoc eo fit, fratres dilectissimi, dum ad veritatis originem non reditur, nec caput quaeritur, nec magistri coelestis doctrina servatur.