How do we know that righteousness is necessary for entering heaven?

Jesus makes a clear declaration in Matthew 5:20: "For I say unto you, That except your righteousness shall exceed the righteousness of the scribes and Pharisees, ye shall in no case enter into the kingdom of heaven." This statement underscores the absolute perfection required for entry into the Kingdom, emphasizing that mere outward adherence to the law is insufficient. The law demands perfect obedience, and God sees the heart, meaning that even thoughts and intentions can render someone guilty. Paul reiterates this principle by affirming that by the law, no flesh will be justified (Romans 3:20). Therefore, recognizing our need for perfect righteousness leads us to understand our reliance on Christ as our righteousness, the only way to be accepted before God.