This is the pattern that we get throughout the scriptures, of the need for a mediator. It begins from almost the very beginning where we read of there being an unseen God, God the Father who is in heaven, and yet we also read of the Lord, one who is by no means lesser God, and yet one who walks with men and women, and talks with men and women. “The doctrine of the mediatorial work of Christ”.
This is something that Job—which is the oldest of all the books of the Bible to be written—speaks of. He says of God the Father, ‘He is not a man as I am that I might answer him’  and in his depression and darkness, he forgets that there is an arbiter, a mediator between him and God, who is able to lay his hand on both God and man as the God-man, which he knows is what he needs . Famously, by the time we get to chapter 19, Job is reminded of what he had lost sight of, and he says— ‘I know that my Redeemer lives.’ 
Do you have times like Job did, where you forget just how amazing it is that there is a mediator, that there is a Redeemer? I’m sure you do. But will you at least ensure that in those times of hopelessness, that you acknowledge what it is you need, it’s one who is human, but is also divine, who can bring you and God together.
Moses himself, as a believer in the Lord Jesus, understood this need for a mediator, and at different points even played-out the part of Christ-like mediator in order to show the people what that meant. As he says in Deuteronomy chapter 5, ‘I stood between the Lord and you to declare to you the word of the Lord’ .
This doctrine is then further explained to us in the books of Moses through the Tabernacle-system that the Living God—Father, Son and Holy Spirit—sets up, and especially through a figure who comes to be called the High Priest, who is for us a multi-faceted presentation of who our Mediator is and what he does.
So, for example, the High Priest wears an outfit, which has as its purpose, the aim of teaching us who the Lord Jesus Christ is (the one who has all authority, access to God, intercedes on our behalf with our names on his heart and shoulders, and the one who is divine). And he performs sacrifices, which again have as their purpose the aim of teaching us that sacrifices will be required in order for this mediation, this go-between work, to take place. 
By the time we get to the New Testament, the Lord Jesus himself is born to the Virgin Mary. He, again, speaks of his work as the one through whom we come to God the Father. He says in John 16, ‘My Father will give you whatever you ask in my name’ . And Paul elaborates on that in his letter to the Ephesians, telling us that through him—through Jesus Christ— ‘we have access to the Father by one Spirit’ .
And by the time we get to the letter to the Hebrews, this access to God through Jesus—the great High Priest—is the big theme of the letter. Famously, the writer tells us that
We have a great high priest who has ascended into heaven, Jesus the Son of God. Therefore, let us hold firmly to the faith we profess. Through him, we can approach God’s throne of grace with confidence, so that we may receive mercy and find grace to help us in our time of need. 
And later in the letter, he tells us that the Lord Jesus ‘always lives to intercede for us’ .
And then the apostle John takes up the very same theme in his first letter, ‘If anybody does sin, we have an advocate with the Father, Jesus Christ the righteous one. He is the propitiation for our sins, and not only for ours but also for the sins of the whole world’. 
 Job 9:32
 Job 9:33
 Job 19:25
 Deuteronomy 5:5 (See also the psalmists taking up that theme, seeing Moses as the Christ-like mediator showing us what Jesus does. ‘Moses stood in the breach,’ we’re told in Psalm 106, ‘before God to keep his wrath from destroying them’ —Psalm 106:23).
 See Hebrews 8-9
 John 16:23
 Ephesians 2:18
 Hebrews 4:14-16
 Hebrews 7:25
 1 John 2:1-2