How do we know salvation is through the heart and not just outward signs?

The apostle Paul emphasizes that true circumcision is of the heart, not just a physical act (Romans 2:28-29). History shows that many relied on external signs, like circumcision or baptism, believing they secured salvation. However, as stated in Jeremiah 4:4, true transformation must occur internally. This heart change is a result of God's grace, leading to genuine repentance and faith. External rituals, like circumcision or baptism, are meaningless without the corresponding work of God within us, demonstrating that salvation is through faith alone, evidenced by a changed life.