The fear of the Lord leads to life,
and whoever has it rests satisfied;
he will not be visited by harm.
The "fear of the Lord" is not a popular concept in modern Christianity. We associate such an idea with pagan religion in which worshippers cringe before an idol in terror or a slave trembling before a cruel master. And yet Scripture portrays the fear of the Lord as something to desire. As the proverb says, it "leads to life."
Some say "fear" should be understood as "respect." Fear does include respect, but there is more to it than that. When Isaiah "saw the Lord" (cf. Isaiah 6:1ff), he did not pay his respect to God; he cried out, "Woe is me!" When John saw "one like a son of man" (cf. Revelation 1:12ff), he did not politely bow his head. And yet, neither man experienced the sense of terror one feels in the presence of mere power or of evil.
C. S. Lewis' depiction of a holy fear is helpful in understanding the fear of the Lord. In Perelandra he describes the feeling of coming in the presence of an "eldil," what we would know as an arch-angel.
“My fear was now of another kind. I felt sure that the creature was what we call 'good,' but I wasn't sure whether I liked 'goodness' so much as I had supposed… Here at last was a bit of that world from beyond the world, which I had always supposed that I loved and desired, breaking through and appearing to my senses: and I didn't like it, I wanted it to go away. I wanted every possible distance, gulf, curtain, blanket, and barrier to be placed between it and me. But I did not fall quite into the gulf. Oddly enough my very sense of helplessness saved me and steadied me. For now I was quite obviously 'drawn in.' The struggle was over. The next decision did not lie with me.”
Lewis picks up on why the fear of the Lord allows one to rest satisfied. For what really happens is not that we break through to good, but that "Good" breaks through to us, forcing us to be helpless, forcing us to let the "next decision" lie with God. There is a sense that we cannot trust God until we fear him; we cannot really love God for who he is until we understand what it is to fear him. We cannot really know fear until we behold the "one like a son of man" dying on a cross for our sin.