The most usual interpretation is that humans are incapable of taking responsibility for there own actions and unable to face the fact that no one is in control of what happens in the world, let alone the universe. Phillip Wylie once wrote, God came into existance when man learned to say "I". Meaning of course,"became self aware". However, there are other opinions. Wikipedia states that it was a statement made in response to the book "Three Imposters". The three imposters being Mohammed, Jesus and Moses.
Voltaire was one of the great thinkers of the Enlightenment, and a supporter of the ideas of Deism. Deism did not say that there was no God but it did not support organised religion. One of the most useful ways to use philosophical ideas is to examine them part by part and compare them to the ideas that we have already formed in our lives. This gives us an opportunity to ask ourselves why we believe what we believe, and whether there are parts of it that we may have outgrown or that may no longer be useful to us. I like Voltaire. He was a cool dude.
(Oh, and Dostoyevsky wrote basically the same thing in The Brothers Karamazov - which could add another layer of understanding to the idea.)
kainsworth, I love you comments. Brings on another 'acid flashback' . I can get so tangle up in my thoughts that I need simple consise words like voltaires. Even then I need the help of beautiful minds like yours.