During an extended visit with Mother Teresa's Missionaries of Charity, Dr. Mary Poplin discovered the depths of sin in her own heart. It happened while Dr. Poplin was trying to care for a five-month-old infant who was deformed, constantly sick, and often miserable. Dr. Poplin always found ways to avoid feeding this child, but one day it was unavoidable. She writes:

When feeding time was over, the babies were falling asleep in their bassinettes, and I was getting ready to go …. I glanced at the infants on my way out [the door] and noticed that undigested formula was dripping out of this child's bassinette. He had thrown up what must have been the entire eight-ounce bottle. Looking around for someone to tell as I left [the room], I saw no one in the infant area, and the few adults in the room had their hands full with other children.

So I decided, with no little struggle, to stay and clean up the mess. I put on my apron again, lifted the baby out of his bassinette and helped him on my shoulder as I began to gather the dirty sheets together and use them to wipe up the mess. As I was cleaning, I heard a muffled sound from the infant in my arms. Tears were pouring out of his eyes, and the only sound he could make was a convulsive sob.

As I looked at him, I saw in myself what Jeremiah called "the desperate wickedness of the heart." I realized I had approached this task with a spirit of resistance and impatience. I had thought very little, if at all, about this child and his needs, other than to be clean. As I threw the sheets into the laundry pile, I began to bathe his little misshapen body and change his clothes. Afterward I held him to me tightly as I … looked at him, rocked him, and prayed …. In a short time, he was asleep ….

I must tell you that the moment I saw him weeping and realized the wretchedness in my heart, I knew it was sin. There was no doubt in my mind that this is what Christ meant when he said, "Out of the heart come evil thoughts." I asked Christ to forgive and change me. In those moments as I rocked the baby, I could feel Christ's work inside my spirit just as surely as if he were sitting next to me.