How do we know that Jesus' death was sufficient for salvation?

The sufficiency of Jesus' death for salvation is firmly rooted in the doctrine of substitutionary atonement, where Christ died not just as a martyr, but as a sacrificial lamb meant to bear the sins of His people. Hebrews 10 emphasizes this by stating that He has perfected forever those who are being sanctified. Jesus' declaration on the cross, 'It is finished,' signifies that His atoning work was complete, securing eternal redemption for those whom the Father gave Him. His act of dying for the elect assures us that all whom He came to save will indeed be saved.