Why is the doctrine of Christ's completed work important for Christians?

The completed work of Christ on the cross, where He purged our sins by Himself (Hebrews 1:3), is foundational for Christian faith. It assures believers that their salvation is secured, as no additional work is needed on their part to earn God's favor. His resurrection and ascension to the Father, where He now intercedes for His people, solidifies our confidence in approaching God. The assurance that Christ has accomplished our redemption means that all honor, power, and glory belong to Him, reminding us that our faith rests on His sufficiency and grace, not our own efforts.