How do we know the doctrine of man's depravity is true?

In Mark 7, Jesus explicitly states that man is not defiled by external actions but by what comes from within, highlighting the wickedness of the human heart. This reality is supported by Scripture that describes the heart as 'desperately wicked' (Jeremiah 17:9) and emphasizes that true righteousness cannot be achieved through human efforts or traditions. Acknowledging human depravity is crucial to understanding the necessity of divine grace for salvation, reinforcing the doctrine that only God can change a person's heart, as expressed in Ezekiel 36:26, where He promises a 'new heart' and 'new spirit.'