How do we know Christ's death truly atoned for sin?

The assurance that Christ's death genuinely atoned for the sins of His people is evidenced in His resurrection. Romans 4:25 states that He was raised for our justification, which means that His resurrection confirms His victory over sin and death. If Christ had not perfectly atoned for sin, He could not have risen, as sin demands death. His resurrection signifies that the payment for sin was accepted by God, providing confidence for believers that their sins are fully forgiven and that they will face no condemnation (Romans 8:34). Therefore, the resurrection is both an assurance and a guarantee of the efficacy of Christ's sacrifice.