How do we know Christ's death guarantees our salvation?

The assurance that Christ's death guarantees salvation lies in the understanding of His atonement. In His sacrifice, He did not merely make salvation a potentiality; rather, He truly justified all His elect from their sins. This is articulated in John 6, where Jesus states that all whom the Father gives Him shall come to Him, and He will never cast them out. When He declares that it is finished, it signifies complete and effective atonement for the sins of His people, ensuring that none for whom He died will perish.