Read Hebrews 9:11–28.
Jesus plays the role of mediator, coming between God and us and enabling us to come into the presence of God
When it comes to interacting with God, humans have always needed a mediator. Since the fall of man, it has been impossible for us to approach God directly. Because of this, God established the priesthood under the old covenant.
Under that system, only those who held that position were allowed to enter the holiest places in the tabernacle. Those places were holy because the presence of God manifested there. But this system was never going to be enough, for two reasons.
First, priests were not holy enough on their own to enter into these spaces. They would have to continually offer sacrifices just for themselves which meant that they would never be able to solve the problem of sin and separation from God on their own. Their sinful nature prevented them from truly being able to represent the interests of God.
The second reason is they were just humans who would one day die. When one died they would have to be replaced, bringing about an end to all the work that had been previously done in their lifetime. At best, this succession of mediators was a band-aid that God allowed until the work could be completed by Christ.
Jesus is the perfect mediator because he is both God and man and can represent the interests of both parties. As God, Christ brings divine justice and mercy to bear on our relationship to our Creator. As man, Christ brings the perfect human obedience we need to be reconciled to God.
Without his mediation our salvation would not be possible.