How do we know Jesus' sacrifice was effective?

The efficacy of Jesus' sacrifice is grounded in its fulfillment of the divine law and His role as the perfect substitute for sinners. In Hebrews 10:19-20, we see that by His death, the veil of the temple was torn, symbolizing that the separation between God and humanity due to sin was removed. Jesus satisfied divine justice through His perfect life and sacrificial death. By fulfilling all righteousness and bearing the consequence of sin, He opened a new way for believers to approach the Holy of Holies, thus ensuring that His sacrifice was indeed effective for atonement.