How do we know Jesus accomplished his work on the cross?

The certainty of Jesus' accomplishment is affirmed in his statements about dying and bringing forth much fruit, as highlighted in John 12:24. His death is not only an event but a cosmic success in securing salvation for those the Father gave him. This echoes the theology of penal substitution where Christ died for the sins of the elect, ensuring that all who believe in him are justified and saved from condemnation. The resurrection further confirms this truth, showing that his death was indeed effective and brought about the full salvation of those entrusted to him. Therefore, his death and resurrection serve as the foundation for the believer's assurance of eternal life.