Jeremiah preached in Jerusalem in the last decades before Babylon burned the city in 587 BC. His audience was a covenant people convinced that temple, lineage, and national identity made them safe. Jeremiah 17 sits in a string of oracles about misplaced trust: cursed is the man who trusts in flesh, blessed is the one who trusts in the LORD. Verse 9 is the diagnostic underneath the curse. The problem is not that Judah has bad information; the problem is that the organ they use to weigh information is itself compromised. Notice that the LXX softens desperately sick to deep — the heart is unsearchable, beyond the reach of its own owner.

From the writers we read together

Nancy Pearcey

cultural apologist, author of Total Truth and Love Thy Body

Pearcey's project for thirty years has been to show that what looks like neutral reasoning is almost never neutral. Every worldview, she argues, begins with a faith commitment — an idol or the living God — and then constructs the arguments that protect it. Jeremiah 17:9 is the theological grounding of her sociology. The heart picks its god first and then hires the mind as defense counsel. This is why exposing bad arguments rarely changes anyone; the arguments were never the foundation. The foundation was a love, and loves are not dislodged by syllogisms.

Which means honest self-knowledge is not something we achieve by sitting longer with our own thoughts. Our thoughts are the lawyers our heart has retained. Jeremiah's question — who can understand it? — gets its answer two verses later: I the LORD search the heart. The only reliable audit comes from outside us. Pearcey would say this is why Christians read Scripture as a mirror rather than as a resource: not to confirm what we already feel, but to be told what we could never have told ourselves.