How do we know that Jesus' mediation is sufficient for salvation?

The sufficiency of Jesus' mediation for salvation is affirmed in Hebrews 10:12, stating, "But this man, after He had offered one sacrifice for sins forever, sat down at the right hand of God." This indicates that Jesus' sacrifice was complete and perfect, satisfying the justice of God on behalf of His people. Unlike the repetitive sacrifices of the Old Covenant that could never take away sin, Christ’s single offering was sufficient for all who believe. By mediating a better covenant, Christ provides not only atonement but also the promise of eternal life, thus securing the salvation of His elect completely and irrevocably.