Why is understanding Christ's accomplishment at the cross important for Christians?

For Christians, recognizing what Christ accomplished at the cross shapes their understanding of salvation itself. It clarifies that salvation is not a mere possibility but a definitive act accomplished by Christ—His death and resurrection secured it fully. The teachings in Hebrews highlight that His sacrifice was effective, taking away sins and establishing a new covenant of grace. This underscores the assurance of believers' salvation and emphasizes reliance on Christ alone rather than any personal merit or works.