A mediator reconciles the differences between two parties and must be equal in stature to both (Jesus Christ was God and true humanity – the hypostatic union). God chose Christ’s work (propitiation), and believers accept Christ’s work (salvation). By so doing, reconciliation is made and a contract is signed. At salvation this is the “seal or signature agreement of the Holy Spirit.”
Christ is the only Mediator between God and man (1 Timothy 2:5,6). Reference the Hypostatic Union.