Q2. In the context of the salvation of all, why do you think Paul emphasizes the roles of Mediator and Ransom? In what way did Christ fulfill both these roles?
When sin entered the world through the fall of man we became enemies of God. Being separated from God we needed redemption for our sins.
Paul emphasizes the roles of Mediator because we couldn't save ourselves and therefore needed an arbitrator, a 'go between' to reconcile the two parties God and humanity.
Not only did Jesus mediate between us, He offered Himself as a Ransom, a sacrifice for us.
Christ fulfilled both roles by offering to die for our sins. He that knew no sin, took our place and died on the cross of Calvary by shedding His blood.
He gave His life as a random for many. Mark 10:45.