How do we know salvation is through Christ's sacrifice?

The doctrine of salvation through Christ's sacrifice is central to Reformed theology and is encapsulated in passages like Hebrews 10:12, which states that Christ, having offered one sacrifice for sins forever, sat down at the right hand of God. Unlike the repetitive sacrifices of the Old Testament, which were insufficient to remove sin, Christ's single offering completed God's redemptive plan, making Him the perfect mediator for His people. This underscores the concept of total depravity and the necessity of a divine substitute to uphold God's justice while providing mercy.