It was 1854, and something was killing thousands of people in London. It must be the bad air, people thought. And indeed, as unseasonable heat baked the sewage-fouled River Thames, the smell grew so bad it became known as “The Great Stink.”

But the worst problem wasn’t the air. Research by Dr. John Snow would show that contaminated water was the cause of the cholera epidemic.

We humans have long been aware of another crisis—one that stinks to high heaven. We live in a broken world—and we’re prone to misidentify the source of this problem, treating symptoms instead. Wise social programs and policies do some good, but they’re powerless to stop the root cause of society’s ills—our sinful hearts!

When Jesus said, “Nothing outside a person can defile them by going into them,” He wasn’t referring to physical diseases (Mark 7:15). Rather, He was diagnosing the spiritual condition of every one of us. “It is what comes out of a person that defiles them,” He said (v. 15), listing a litany of evils lurking inside us (vv. 21–22).

“Surely I was sinful at birth,” David wrote (Psalm 51:5). His lament is one we can all voice. We’re broken from the beginning. That’s why David prayed, “Create in me a pure heart, O God” (v. 10). Every day, we need that new heart, created by Jesus through His Spirit.

Instead of treating the symptoms, we must let Jesus purify the source.