The biblical fear of God runs the gamut from a mild respect through a deep, abiding, and reverential awe to sheer terror—a terror that causes the skin to crawl, the hair to stand on end, the throat to release a scream, the bowels to move, or the body to faint or collapse, groveling on the ground in a vain attempt to disappear, as Isaiah did (Isaiah 6:5). Fear can be an extremely effective motivator. Many of us have seen, heard, or experienced something so fearsome that the "fight or flight" response kicked in. The terror moved us to take immediate steps to defend ourselves physically or seek protection by running from the danger.
However, fear can also be a two-edged sword. Though it undoubtedly motivates, it can also paralyze us into doing nothing but rolling ourselves into a fetal position. In relation to God, a most subtle and deceptive problem is that, because we cannot literally see Him, we do not feel that responding to Him is of immediate concern. In this way, fearing God is not like our reaction to a lion suddenly jumping out of the jungle and confronting us on the path.
The result, though, can be just as deadly! The major difference is timing. Because of God's patience, the end comes more slowly if our reaction is not correct and no repentance occurs. Nonetheless, our relationship with God may die because not having the proper fear invites apathy and procrastination. Our fear must have enough of an "edge" that we are motivated to act correctly—but not so much that we are paralyzed into inaction. That "edge" grows as true knowledge of Him increases.
Some may think that God does not require of us this level of fear. However, for "trembles" in Isaiah 66:2, the Septuagint uses a Greek word that means a reverential awe that has an "edge" to it. God will "look on" a person who has this kind of fear. Without the proper fear of God in us, there will be precious little reciprocation of His love shed abroad in our hearts (Romans 5:5).
Romans 12:1 makes it clear that overcoming in this way of life requires sacrifice. We all know how costly sacrifice is sometimes. Our apprehension of making sacrifices required to submit to God's will stops us on occasions, motivating us to draw back from obeying. In this case, the problem is fearing the wrong thing! Sometimes, the degree of the fear of God we need comes close to sheer terror because we are often so difficult to convince!
However, what is necessary as a matter of course is an abiding reverential awe.