The key question is this:
if God made us, why do we need a mediator to make a way between us and Him? Why can't we just freely know Him and talk to Him?
This is really the key question of the whole Bible! And answers can be found from very early on in Scripture.
In Genesis 1-2, it is made clear that man has a special role to play in God's amazingly vast and varied creation. God breathes life into the man, and says He has made men and women in His image. Adam and Eve enjoy the garden of Eden but most of all they enjoy fellowship with God, who walked with them in the garden. They were perfect and sinless in a perfect creation.
However, it's worth saying here that even in their perfect, sinless state, they did not deserve the privileges they were given. However amazing humans are, they are nothing in comparison to the great and awesome God who spoke an entire universe into being. 'and God said, "Let there be light...' (Gen 1:3) However wonderful we are, God is far more wonderful. That He chose to make us and He chose to walk in the garden are wonderful examples of His grace- His undeserved favour given to those who do not deserve it.
We see further evidences of His grace in the beautiful creation that surrounds us. Look at all the wonderful varieties of butterfly, bird and flower. Look at the astounding intricacy and delicacy of bees building a honeycomb, and we can see that God has made us an interesting, complex and beautiful creation. He didn't have to create colours, shades and tones. He didn't have to make all the textures and sounds and movements in creation. But He did, out of His infinite grace and His creative wisdom and imagination.
Psalm 8 really encapsulates the awe we should feel when we look at the world around us:
'When I look at your heavens, the work of your fingers, the moon and the stars, which you have set in place,
what is man that you are mindful of him, and the son of man that you care for him?' (v3-4)
When we compare ourselves to the gigantic splendour of the sun and stars, we get some perspective of how small we are in this universe, and of how much greater God is. We don't deserve His grace and favour, yet He still gives it! And even when we rebel against Him...
Because that's the story of Genesis 3. Adam and Eve, despite their wonderful privileges, did the one thing they were asked not to do. They ate the fruit and their sin separated them from God. They were exiled from Eden.
Ever since then, men have needed a way to be made right with God. And in the rest of the Bible, there is an increasing revelation of how God makes that possible. In the rest of Genesis, God chooses Abraham to make a covenant with him and his future descendants. All an act of grace. Abraham's descendants, the Israelites, end up in slavery in Egypt, and God raises up Moses to lead them out. Moses becomes a mediator, the one who speaks to the LORD and conveys His commandments to the people. But Moses feels his own inadequacies as a mediator. He longs for the day when God's Spirit will be poured out on all believers (Num 11:29). Over the next generations, God raises up leaders for the people, from Joshua to the judges like Samuel, and then kings like David who sought God's heart. But there are many kings who lead Israel into further idolatry and rebellion, and the Old Testament ends with a much diminished Israel, a remnant, post-exile to Babylon, looking forward to the day when God will make things right again with His anointed one: the Christ.
Jesus is the mediator that the whole of Scripture points towards:
'For there is ...one mediator between God and men, the man Christ Jesus.' (1 Tim 2:5)All other human mediators before this point had their failings (Moses disobeyed God by striking the rock, David committed adultery with Bathsheba and murdered her husband Uriah, to provide just two examples). Jesus was completely without sin, so therefore His mediation was perfect. Hebrews teaches that He acted like a High Priest... in fact, He is the High Priest to end the Levitical priesthood for ever, because He is the High Priest of a new covenant which is superior to the old and replaces it (Heb 7:22,27; Heb 8:6). He made the perfect sacrifice for sins once for all, and then sat down at the right hand of the Father (Heb 8:1). His unique status as the Son of God enables Him to mediate for us in a way that no one else could. He was fully man and this meant that He could fully take the penalty for sin in His flesh, without at all deserving it because He resisted sin. 'God made Him who had no sin to be sin for us, so that in Him we might become the righteousness of God' (2 Cor 5:21).
Let's go back to Psalm 8. The Psalmist continues:
'Yet you have made him a little lower than the heavenly beings and crowned him with glory and honor.
You have given him dominion over the works of your hands; you have put all things under his feet,
all sheep and oxen, and also the beasts of the field,
the birds of the heavens, and the fish of the sea, whatever passes along the paths of the seas.'
But we find out in Hebrews 2 that this passage actually refers to Jesus! The writer quotes it and explains: 'In putting everything under Him, God left nothing that is not subject to Him.' (Heb 2:8) Jesus had to be 'made like His brothers in every way, in order that He might become a merciful and faithful high priest in service to God, and that He might make atonement for the sins of the people' (Heb 2:17) This is why we need a mediator. We need Christ's substitutionary atonement for us, dying on the cross for our sins, and we need His imputed righteousness, the positive effect of His holy life, projected onto us so that in God's sight we are made righteous.
These are massive concepts! And there is so much complexity and depth to them. But for now I want to keep it within reasonable reading length, and I realise I have probably moved far beyond that already.
To sum it up: even if we were perfect, to know God and be in relationship with Him would be a gift of His grace (and He was willing to give this freely, as Genesis 1-2 show). Because we are sinful, to know God and be in relationship with Him is only possible through the mediation of Jesus Christ. We need Him to take away our sin, and we need Him to clothe us with His righteousness so we can stand before God and be made holy and blameless in His sight (Eph 1:4).
