How do we know man's heart is corrupt according to the Bible?

In Matthew 15:18-20, Jesus states that 'those things which proceed out of the mouth come forth from the heart; and they defile the man.' The passage reveals that it is out of the heart that evil thoughts, murders, adulteries, and other sins arise, demonstrating man's inherent corruption. This biblical teaching underscores the necessity of a transformed heart through regeneration, as no outward actions alone can cleanse a sinful nature. Understanding this reality is essential for recognizing the need for a Savior.