How do we know Jesus' death on the cross was effective?

The effectiveness of Jesus' death is established clearly in Scripture, particularly in Hebrews 10:10, where it states that by His will, we are sanctified through the offering of His body once for all. Unlike the repetitive sacrifices of the Old Testament, which could never take away sin, Christ's sacrifice was once and for all, ensuring that His death was sufficient and effective for atonement. Acts 2 and 4 further emphasize that His death was by God's predetermined plan, fulfilling His will and securing eternal redemption for His people.