Exodus 19:24
The Lord replied: go down and bring Aaron up with you. But the priests and the people must not force their way through to come up to the Lord, or he will break out against them. God accepts Moses' clarification and adds a provision: bring Aaron. Aaron's presence with Moses at the summit is the beginning of the priestly partnership that will be formally established in Exodus 28–29. Aaron will be Israel's first high priest; his invitation to the mountain before the priesthood is even instituted anticipates the role he will fill. The repeated warning — do not force their way through — is the grace of repeated warning: God gives the same caution twice rather than allowing the violation to occur unwarned.