The Ways of the Devil

In hac autem, dilectissimi, misericordia Dei, cujus erga nos magnitudinem explicare non possumus, multa sollicitudine praecavendum est Christianis ne diabolicis iterum capiantur insidiis, et eisdem rursus, quibus renuntiaverunt, erroribus implicentur. Non enim desinit hostis antiquus, transfigurans se in angelum lucis, deceptionum laqueos ubique praetendere, quoquo modo fidem credentium corrumpat, instare. Novit cui adhibeat aestus cupiditatis, cui illecebras gulae ingerat, cui apponat incitamenta luxuriae, cui infundat virus invidiae; novit quem moerore conturbet, quem gaudio fallat, quem metu opprimat, quem admiratione seducat; omnium discutit consuetudines, ventilat curas, scrutatur affectus; et ibi causa quaerit nocendi, ubi quemque viderit studiosius occupari. Habet etenim multos ex eis quos tenacius obligavit, aptos artibus suis, quorum ad alios decipiendos et ingeniis utatur et linguis. Sanctus Leo Magnus, Sermo XXVII

But in this mercifulness of God, dearly beloved, the greatness towards us which we cannot explain, Christians must be very careful lest they be caught again in the Devil's wiles and again become ensnared in the errors which they had renounced. Indeed the old enemy does not cease to transform himself into an angel of light that he might place everywhere the snares of deceptions and in every place corrupt the faith of believers. He knows to whom to apply the heat of greed, whom to beset with the allures of the belly, near whom to set the temptations of luxury, in whom to infuse the poison of envy; he knows whom to distress with grief, whom to delude with joy, whom to crush with fear, whom to seduce with admiration. He sifts everyone's habits, winnows everyone's cares, pries into everyone's affections; and there he seeks a chance to harm when he sees someone most keenly occupied. And indeed of these he has many whom he has bound more tightly because they are suited for his schemes, that he may employ their minds and tongues to deceive others. Pope Leo the Great, Sermon 27