A mediator is someone who helps two parties connect or communicate with each other. In the Bible, mediators helped people approach God and understand God's messages. They did not try to negotiate compromises but instead acted with God's authority to help people know God better.
In the Old Testament
Job wanted someone to be a mediator between him and God. He said: “God is not subject to death like me, so I cannot argue with him or take him to trial. If only there were a mediator who could bring us together. There is none. The mediator could make God stop beating me. I would no longer live in fear of his punishment. Then I could speak to him without fear. I cannot do that in my own strength” (Job 9:32–35; translated here from the Septuagint).
More familiar is the mediation of teaching about God's character and will. God gave his covenant (agreement with his people) through angels and through Moses (Exodus 20:18–21; Deuteronomy 33:2; Acts 7:53; Galatians 3:19) In Hebrews 6:13–17, God acted alone when making his promise to Abraham. The terms of the covenant law were described by prophets who received messages directly from God (or “stood in God’s council”). The priests also spoke God’s messages by prophecy, casting lots, and speaking blessings (Deuteronomy 10:8; 33:8–10; 2 Chronicles 15:3; Jeremiah 23:10–11, 18–22, 31–34; Micah 3:11; Malachi 2:7). It is not clear what casting lots was, but it was a way to identify God's will by using sticks of different length or flat rocks.
Priests had a special role as mediators in worship. This started with Moses (Exodus 24:4–8). It continued with other trained priests (28:1). Because of Israel’s emphasis on the holiness of God, sacrifices for sin or the “covering” of sin were important for priestly mediation. The priest represented people before God. They brought the people’s repentance, confession, and prayers for forgiveness to God. The priests had the names of the tribes written on his shoulders and on a plate the he wore on his chest. The priest also represented God, offering his favor, forgiveness, and protection to the people (see Hebrews 5:1–4; 7:27–10:11).
In the New Testament
Jesus was described as a mediator in several ways. First, he was seen as a prophet who spoke for God and made God known to people (Mark 6:15; 8:28). The title "mediator" is used specifically for Jesus when talking about the new covenant he established between God and people (Hebrews 8:6; 9:15; 12:24). The one other use is 1 Timothy 2:5. Here Paul says the unity of God requires a single mediator with no equal. This is Christ.
Jesus “gave Himself as a ransom for all” (1 Timothy 2:6). This essentially priestly function is the theme of Hebrews. The book of Hebrews explains that Jesus is uniquely qualified to be the High Priest for his people because he:
Is God's Son
Was appointed by God
Never sinned
Suffered and was tempted like humans
Understands and cares for people
Always obeyed God
As a priest, Jesus offers a perfect sacrifice. He lives forever to work on behalf of those who draw near to God through him. This role as mediator places Jesus at “the right hand of God.” His mediation (or intercession) for people is also mentioned in Romans 8:34. According to ancient Greek commentators, the New English Bible, and other important sources, "advocate" (from the Greek paraklētos) in 1 John 2:1 is also likely a reference to Jesus's mediating work. His sacrifice as a mediator is mentioned in Matthew 26:28, John 1:29, Romans 3:25, and 1 John 1:7, 2:2, and 4:10.
The New Testament repeatedly teaches that Jesus is essential for everything we receive from God. Jesus became poor to help us, died for us, and rose from death "for us." Jesus is our peace and access to God. He restores us to a good relationship with God. He is the payment for our sins. Because of him, we have grace and truth and can pray. “All spiritual blessings” are “through him,” “in him,” “through his blood,” and “in his name.”
The purpose of God focuses on Jesus. Jesus mediated at creation and at redemption (Colossians 1:15, 22). Jesus perfectly shows what God is like. Only Jesus and the people Jesus teaches can know God the Father. The only way to come to God is through Jesus, and Jesus is the only one who can save people.
Jesus's mediation is the completion and end of all mediators between God and humankind. The book of Hebrews explains that Jesus is greater than all other mediators, including angels, Moses, and priests in the family line of Aaron (the Levites). Jesu's priesthood is an eternal priesthood, like Melchizedek’s. His sacrifice cannot be repeated. It was “once for all time.” By his sacrifice, we have been set apart to God “for all time.”
The covenant Jesus established between God and people offers better promises, sacrifice, safety, and hope (Hebrews 7:19; 8:6; 9:1, 11–15). Jesus's role as a mediator is better than all others. It can never be replaced. He is a priest forever and with no one to equal him (compare 1 Timothy 2:5).
Without using the priestly comparison, John argues the same truth. The gap between God and humans has been crossed. Jesus crossed this gap in a final and complete way by becoming human. Instead of acting as a messenger between God and people, Jesus unites them by becoming human himself.
Jesus was the mediator at the beginning at creation. Jesus is himself the Word. He teaches us God's thoughts, fully represents God's message, and shows God's power. No one has seen God at any time. As God's unique, divine Son, Jesus makes God known (John 1:18). From the human side, Jesus prays for the disciples (chapter 17). Jesus obeys God perfectly. He gives his life for his people. He offers the perfect sacrifice that takes away the sin of the world.