In today's reading we see fear exemplified 3 times. First, the people tremble with fear at God's presence. Second, Moses instructs the people to 'not be afraid." And, finally, Moses tells them “for God has come in this way to test you, and so that your fear of him will keep you from sinning!”
Fear is a funny thing, especially when it comes to God. God, who has established this relationship of love for God's people also commands enough respect or fear that God's children know that God can bring blessings and curses. Much like a loving parent that establishes good boundaries of reward and correction, God is to be feared because God can bring punishment and blessing. A healthy respect of your parents taught you what boundaries existed. A healthy respect of the Lord keeps us in right relationship with the God who does love us. Often times we don't discuss this respect or fear of the Lord because we like to err on the side of grace but as Paul wrote in Romans 6, "shall we continue to sin so that grace may abound?....CERTAINLY NOT!" the fear of the Lord is the beginning of wisdom because it helps us understand the boundaries of the covenant agreement God has given us: "I am the Lord your God who delivered you from the land of Egypt the Land of Slavery. I will be your God and you will be my people." The reminder is the fear that God put slavery (of overproduction and sin) to death by punishing the Egyptians and Pharaoh, swallowing them into the parted sea, but also promised to bring these children of God into a new land. Blessing and curses. Respect!