The Strolling Saint by Rafael Sabatini

At first I seemed to make good progress in my quest after grace, and a certain solatium of peace descended upon me, beneficent as the dew of a summer night upon the parched and thirsty earth. But anon this changed and I would catch the thoughts that should have been bent upon pious meditation glancing backward with regretful longings at that life out of which I had departed.

I would start up in a pious rage and cast out such thoughts by more strenuous prayer and still more strenuous fasting. But as my body grew accustomed to the discomforts to which it was subjected, my mind assumed a rebellious freedom that clogged the work of purification upon which I strove to engage it. My stomach out of its very emptiness conjured up evil visions to torment me in the night, and with these I vainly wrestled until I remembered the measures which Fra Gervasio told me that he had taken in like case. I had then the happy inspiration to have recourse to the hair- shirt, which hitherto I had dreaded.