How do we know that Jesus' sacrifice is effective?

The singular and perfect nature of Christ’s sacrifice is emphasized in Hebrews 10:14, which declares that by one offering He has perfected forever those who are sanctified. This demonstrates the efficacy of His atonement; unlike the repeated sacrifices of the Old Testament, which could never take away sin, Christ's sacrifice was sufficient once for all. As such, every believer is viewed as perfect and without blemish in God’s sight. This assurance is rooted in the identity and power of the one who offered the sacrifice—Jesus, the Son of God—making the work effectual for those whom He died for.