Set it apart as holy for God is holy

Exodus 19:16-25
Set it apart as holy.
There was thunder and lighting, with cloud over the mountain, and a very loud trumpet blast. Everyone in the camp trembled.
Thunder, fire, earthquake and lightning herald(先鋒) God's presence and demonstrate his power.
The Lord God, holy, awesome, unapproachable, speaks.
Why?
God is Holy so set it apart as holy when we come to Him.
Fear the Lord for He is powerful and great, he rules over the whole universe.
The priests dis not exist as an order until after Sinai.
How?
Set my life apart as holy before the Lord!