How do we know Jesus' teachings on the heart are true?

The accuracy of Jesus' teaching about the heart's role in defilement is affirmed through biblical prophecy and the continual human experience of sin. In Mark 7, He clearly states that what comes from within, such as evil thoughts and actions, is what defiles a person. This teaching is consistent with the Old Testament understanding of sin and the New Testament revelation of the human condition. It shows that religion focusing merely on external compliance misses the deeper issue—our need for a transformed heart through faith in Christ.