St. John Chrysostom: Paul continued to observe the Law and to endure many a toil...

Paul continued to observe the Law and to endure many a toil; he patiently put up with many journeys and hardships; he surpassed all his contemporaries in the exact observance of that way of life. But after he achieved the heights of that life and came to realize that he was doing all this for his own hurt and destruction, he immediately changed. 

He did not say to himself: "What is this? Am I to lose the reward for this great zeal of mine? Am I to waste all this work?" Rather he was the quicker to change for the very reason that he might continue to suffer that loss. 

He scorned justification by the Law so that he might receive the justification of faith. And so he loudly proclaimed: "The things that were gain to me I have counted as loss for Christ."'

St. John Chrysostom