How do we know that Christ's atonement was sufficient for salvation?

The doctrine of the sufficiency of Christ's atonement rests on His significant declaration 'It is finished' as recorded in John 19:30. This statement confirms that every requirement of the law has been satisfied and the debt for sin has been completely paid through His sacrifice. Colossians 2:13-14 further elaborates, stating that God 'forgave us all our trespasses' and 'blotted out the handwriting of ordinances that was against us.' This fully establishes that there is nothing left for believers to achieve by their works. The completeness of Christ's work on the cross assures us that all for whom He died are guaranteed salvation and reconciliation with God.