Fear not That is, Think not that this thunder and fire are designed to consume you. God is come to prove you To try how they would like dealing with God immediately, without a mediator, and so to convince them how admirably well God had chosen for them in putting Moses into that office. Ever since Adam fled, upon hearing God's voice in the garden, sinful man has not been able to bear either to speak to God, or hear from him immediately.
Related Commentaries of Exodus 20:20
Exodus 20:20
20 And Moses said unto the people, Fear not: for God is come to prove you, and that his fear may be before your faces, that ye sin not.