How do we know that Jesus' sacrifice accomplished salvation?

The effectiveness of Christ’s sacrifice is affirmed throughout Scripture, particularly in John 17:4 where Jesus says, 'I have finished the work which you gave me to do.' This indicates that His atoning work was not an attempt but a complete accomplishment. In contrast to other sacrifices that could never take away sin, Christ's one offering was sufficient to remit the sins of the elect forever (Hebrews 10:12). The consistency in Scripture about Christ's mission underscores the completed task of salvation, leaving no room for the notion that He died in vain.