John Cassian, The Institutes XII.10: How no one can obtain perfect virtue and the promised bliss by his own strength alone

For the will and course of no one, however eager and anxious, is sufficiently ready for him, while still enclosed in the flesh which warreth against the spirit, to reach so great a prize of perfection, and the palm of uprightness and purity, unless he is protected by the divine compassion, so that he is privileged to attain to that which he greatly desires and to which he runs. For “every good gift and every perfect gift is from above, and cometh down from the Father of lights.” “For what hast thou which thou didst not receive? But if thou hast received it, why dost thou glory as if thou hadst not received it?”