No one, however fervent, however desirous, can have a will so disciplined, a course so ordered, that in spite of the flesh warring against the spirit he can still attain to so great a prize of perfection and to such a reward of sinless purity, unless he be protected by the divine mercy to enable him to have the merit to arrive at last at that which he so greatly desires and runs to reach. For ‘every good gift and every perfect gift is from above, coming down from the Father of lights (James 1:17). And, ‘what hast thou that thou didst not receive? But if thou didst receive it, why dost thou glory, as if thou hadst not received it?’ (1 Corinthians 4:7).
~St John Cassian
Prayerful Life 