How do we know the sufficiency of Christ's sacrifice is true?

In Hebrews 9:26, it states that Christ appeared once at the end of the world to put away sin by the sacrifice of Himself. This notion of sufficiency underscores that unlike the numerous animal sacrifices of the Old Testament, which were repeated over and over, Christ's single sacrifice was complete and fully satisfied God's justice. Romans 8:29-30 further supports this by outlining the unbreakable chain of salvation from predestination to glorification, affirming that all whom Christ died for will surely be saved. Hence, His sacrifice is not only sufficient but also perfect for securing salvation for God's people.