They are led away against their will or rather without knowing it, into the law of sin and death, and…are kept back by actions which…which are good and right though earthly, from the vision of God.
Then they have something to groan over constantly to the Lord. They have something for which indeed to humble themselves, and in their contrition to profess themselves not in words only but in heart, sinners.
And for this, while they continually ask of the Lord’s grace pardon for everything that day by day they commit when overcome by the weakness of the flesh, they should shed without ceasing true tears of penitence.
For they see that, being involved even to the very end of their life in the very same troubles, with continual sorrow for which they are tried, they cannot even offer their prayers without harassing thoughts.
They know by experience that through the hindrance of the burden of the flesh they cannot by human strength reach the desired end, nor be united according to their heart’s desire with that chief and highest good, but that they are led away from the vision of it captive to worldly things.
Therefore they betake themselves to the grace of God, “Who justifieth the ungodly” (Rom. 4:5) and cry out with St Paul: “O wretched man that I am! Who shall deliver me from the body of this death? Thanks be to God through our Lord Jesus Christ” (Rom. 7:24-25).
For they feel that they cannot perform the good that they would, but are ever falling into the evil which they would not, and which they hate, i.e., wandering thoughts and care for carnal things.
[…] And they “delight” indeed “in the law of God after the inner man,” which soars above all visible things and ever strives to be united to God alone.
But they “see another law in their members,” i.e., implanted in their natural human condition, which “resisting the law of their mind” (Rom. 7:22-23), brings their thoughts into captivity to the forcible law of sin, compelling them to forsake that chief good and submit to earthly notions.
These, though they may appear necessary and useful when they are taken up in the interests of some religious want, yet when they are set against that good which fascinates the gaze of all the saints, are seen by them to be bad and such as should be avoided, because by them in some way or other and for a short time they are drawn away from the joy of that perfect bliss.
John Cassian (c. 360-435): Conferences 23, 10-11.