Selected quotes from St. John Cassian

"It should be known, however, that the unclean spirits obey human beings in two ways. Either they are rendered submissive to the holiness of the faithful through divine grace and power or, having been soothed by sacrifices and by certain songs of the impious, they fawn over them as over friends."

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"However, of this much we must be sure. Never by our sole diligence or zeal nor by our most tireless efforts can we reach perfection. Human zeal is not enough to win the sublime rewards of blessedness. The Lord must be there to help us and to guide our hearts toward what is good. Every moment we must join in the prayer of David: 'Direct my footsteps along Thy paths so that my feet do not move astray' (Ps. 16:5) and 'He has settled my feet on a rock and guided my footsteps' (Ps. 39:3) - all this so that the invisible guide of the human spirit may direct back towards love of virtue our free will, which in its ignorance of the good and its obsession with passion is carried headlong into sin."

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"We are often indifferent to our brethren who are distressed or upset, on the grounds that they are  in this state through no fault of ours. The Doctor of souls, however, wishing to root out the soul's excuses from the heart, tells us to leave our gift and to be reconciled not only if we happen to be upset by our brother, but also if he is upset by us, whether justly or unjustly; only when we have healed the breach through our apology should we offer our gift."