In Chapters 28-29 we see the institution of the priesthood, with Aaron installed as the first high priest. The priesthood will be the mediators between God’s people and God. It is only through the priest that the people of God can meet God. It is only through the priest that the sins of the people can be atoned for through the death of a sacrifice. The holiness of God and the sinfulness of man means that in order for God to dwell with his people a mediator is necessary. The issue of course is that every priest themselves is sinful, they themselves are in need of sacrifice and atonement. All of this points towards our need for a better mediator, it points to our need for Jesus.
Cambridge: Exodus