What does the Bible say about the source of our sin?

According to Matthew 15:18-20, Jesus clarifies that it is not what enters the mouth that defiles a person, but rather what comes from the heart. This means that sin originates within us, being a reflection of our inner thoughts, affections, and will. As Romans 3:23 states, 'For all have sinned and come short of the glory of God,' indicating that the problem of sin is universal and deeply rooted within human nature. Therefore, understanding the source of our sin is crucial for recognizing our need for salvation and the grace of God in addressing our heart condition.