How do we know that humans are inherently sinful?

The inherent sinfulness of humanity is a foundational doctrine in Reformed theology. Jeremiah 17:9 states, 'The heart is deceitful above all things, and desperately wicked; who can know it?' Jesus reinforces this by teaching in Matthew 15:19 that 'out of the heart proceed evil thoughts, murders, adulteries...' This reveals that our sinful actions stem from an unclean heart. Thus, the doctrine of total depravity asserts that every aspect of humanity has been affected by sin, making humanity incapable of achieving righteousness on its own. Only through God's intervention can one be reconciled and made righteous through faith in Christ and His atoning work.