You see how he made the chief part of the struggle depend upon himself, that is upon his flesh, as if on a most sure foundation, and placed the result of the battle simply in the chastisement of the flesh and the subjection of his body. “I then so run not as uncertainly.”
He does not run uncertainly, because, looking to the heavenly Jerusalem, he has a mark set, towards which his heart is swiftly directed without swerving.
He does not run uncertainly, because, “forgetting those things which are behind, he reaches forth to those that are before, pressing towards the mark for the prize of the high calling of God in Christ Jesus” (Phil. 3:13-14), whither he ever directs his mental gaze, and hastening towards it with all speed of heart, proclaims with confidence, “I have fought a good fight, I have finished my course, I have kept the faith” (2 Tim. 4:7).
And because he knows he has run unweariedly “after the odour of the ointment” (Cant. 1:3) of Christ with ready devotion of heart, and has won the battle of the spiritual combat by the chastisement of the flesh, he boldly concludes and says, “Henceforth there is laid up for me a crown of righteousness, which the Lord, the righteous judge, will give to me in that day.”
And that he might open up to us also a like hope of reward, if we desire to imitate him in the struggle of his course, he added: “But not to me only, but to all also who love His coming” (2 Tim. 4:8).
He declares that we shall be sharers of his crown in the day of judgment, if we love the coming of Christ—not that one only which will be manifest to men even against their will; but also this one which daily comes to pass in holy souls—and if we gain the victory in the fight by chastising the body.
And of this coming it is that the Lord speaks in the Gospel. “I,” says He, “and my Father will come to him, and will make our abode with him” (John 14:23).
And again: “Behold, I stand at the door and knock: if any man hear my voice and open the gate, I will come in to him and will sup with him, and he with me” (Rev. 3:20).
John Cassian (c. 360-435): Institutes 5, 17.