me·di·um (mee-dee-uhm) n.
An intervening substance through which something is transmitted or carried on. An agency by which something is accomplished, conveyed, or transferred.

me·di·a·tor (mee-dee-ey-ter) n.
One who acts as an intermediary, esp. in order to resolve or reconcile differences between conflicting parties by an agreement, a settlement, or a compromise.

Which one is the church? Is it both? Or neither? What is the difference?

Traditonally, the Church has assumed both roles in various ways. As the body of Christ it could be considered the substance through which God’s salvation is transmitted, and his truth carried on. Jesus gave authority, or agency, to the apostles, so that they could accomplish his work and convey the gospel message to the ends of the Earth.

Is the Church always a necessary intervening substance? Does God’s grace pass through the Church, or is that flow direct to an individual after the message of grace has been conveyed by the Church?

Does the Church stand between God and the individual? Does it act as an intercessor between God and man? Or does that role exclusively belong to Jesus? Certainly Jesus, once for all, settled and reconciled our differences. Is there more to be done by the body of Christ now?

If the Church is mediator, does it also control the distribution of grace? Can it withhold grace from an individual, or establish criteria that the individual must meet to receive God’s grace? Or is God’s grace freely offered to all? Is the mediator role ongoing, or is it only effective in the process of conversion?