Why is Christ's finished work essential for salvation?

Christ's declaration 'It is finished' on the cross signifies the completion of His work of redemption, conveying that He has borne the penalty for sin and fulfilled all righteousness required by the law. This work was not in vain; it secured salvation for all whom He came to save, as attested throughout the New Testament. The assurance of salvation does not rest on human effort but solely on Christ’s work, which was sufficient to cover even the depth of sin. Believers can confidently rest in this truth, knowing they are accepted on the basis of Christ's righteousness alone, not their own.