Jeremiah 17:9

The human heart is deeply deceptive and sick, beyond our own ability to fully understand. In Scripture the "heart" is the inner center of thought, will, and desire, not merely feelings. Jeremiah's diagnosis is unsparing: the heart is "deceitful above all things," meaning it can mislead even its owner, dressing up wrong motives as good ones. "Desperately wicked" pictures something gravely sick or twisted. The closing question, "who can know it?" admits that we cannot fully map our own inner depths; we are capable of self-deception we never detect.

This sober honesty is not meant to crush but to redirect. If we cannot finally trust our own assessment of ourselves, we need someone who sees us truly. The very next verse answers the question -- the Lord searches the heart and knows it. So this verse drives the reader from self-confidence to God-dependence. It guards against the easy assumption that our intentions are always pure. Rather than encouraging despair, it invites humility, self-examination, and the prayer that God would reveal and heal what we cannot even see in ourselves.