Why is Christ considered a better mediator?

In Hebrews 9:15, we learn that Christ is the mediator of the New Testament, which brings the promise of eternal inheritance to those who are called. His mediation is unique because all blessings of this New Covenant are secured through His sacrificial death. Unlike the Old Covenant mediated through the law, which could only serve as a temporary covering for sin, Christ’s death not only redeems but also guarantees the fulfillment of God's promises to His people. Hence, His role as mediator is crucial in the administration of redemptive grace and the assurance of eternal life.