Men invented the idea of gods to explain what they could not explain any other way.
Now the need for gods has gone, man cannot explain everything but science has come up with enough answers that seem to sketch out much of the important features in our Universe, there seems no place for God to be hiding.
Next to my computer is a map of the world. It has most of the continents placed in roughly the right place. The shape of South America is clearly discernible. North America is a mess. It has Virginia marked but little else has its current name. Much of the detail is obvious guesswork. It is interesting to note that the map maker guessed right in putting a southern continent covering the pole but showing the North Pole with no land. He got the size of the southern continent a bit wrong though, Antarctica is not bigger than Asia or joined to the northern tip of Australia or Tierra del Fuego. I see this map as a reasonable metaphor for mankind's current knowledge of the Universe, we know a lot, we have made some good guesses about the rest. Time will prove many guesses wrong. But we know enough to do the equivalent of sailing from Europe to Japan without expecting to find dragons in our way.
Good stories never die. God continues to have a hold on us because it is a good story. The idea of God has been with us for thousands of years. Good stories get re-told. The story of God is a meme, an idea that has what it takes to get itself replicated. It has a hold on us because it is a meme complex, a series of ideas that get bundled together and get passed on together.
Nobody hears about God in isolation, suddenly coming across the idea for the first time in a theology lecture at the age of 18. The idea of God is so prevalent in our society that we never really learn it in the way we learn a foreign language, we learn it in the way we learn our own language. We learn it before we have become critical thinkers, it pollutes all our thoughts the way PCBs pollute our mother's milk. Before we know for ourselves if God exists or not we know where he lives, what he does to little boys and girls that are naughty and that he made all the flowers and the the birds and if we are bad he will tell Santa Claus not to come to give us any presents. We learn all the baggage that comes along with the central idea before we are capable of analysing the central concept. Before we are capable of knowing what a religious experience is we know that the Bible is always right. We have leaned lots of Bible stories and we have been armed with the religious inoculation against atheism and other religions.
Here is a short list of ideas that were well established in my head before I was old enough to decide I didn't believe a word of it:-
"Don't tempt me satan." An excellent all purpose inoculation against reasoned argument from any quarter. The smart thing is that the more intelligent the challenge to Christian orthodoxy the more obviously diabolical the source is shown to be. The fact that an argument for atheism appears to be reasonable proves it must come from the horned deceiver himself. If this piece does not convince you from your God fearing ways it is because I am only one of the master's lesser imps, the fallen angel himself is busy writing television sit-com scripts and rock lyrics. (Note, that was IRONY)
Unbelievers go to Hell. This is a classic memetic strategy, it gives reward to those that pass on the meme. If you know that your actions will save a soul from torment it is your duty to act. If catching that soul before they are old enough to resist indoctrination improves the chances that the soul will be saved then not to indoctrinate would surely be a sin. If frightening children saves their soul then it is your duty to do it. Accepting that logic is only a small step from accepting the need to marry your niece when she is thirteen to keep her in the bosom of the true faith, or of killing your whole family to save their souls from the satanic messages on MTV.
Suffer little children to come unto me. This means allowing children to learn the wonderful works of Jesus. No parent is going to be convinced by a conspiratorial idea to tell their children to believe something early while there is a chance the child will accept it without thinking. That is a poor reward for passing on the message. But Jesus is quoted as saying himself that children must be allowed to learn the message early, for their own good. Tied up with this is the thoroughly evil idea that the souls of unbaptized dead children will be denied a place in heaven.
The Bible is the word of God. This is another key belief in the interlocking series of ideas that help perpetuate religion. The Bible is the revealed word of God, revealed to the writers of the Bible, which contains the revealed word of God. Remember, you learned this before you learned that tautology was a weak form of argument, and you learned it from the experts in the Bible, which is the revealed word of God, they must know what they are talking about. They are men of God. They know the Bible. The Bible is the Gospel Truth after all. If you believe that the Bible contains the word of God then you can prove your point, look! There it is, in the Bible! I can give you chapter and verse, what more proof do you need?
Faith is a virtue. Belief without proof is a virtue for the religious. To the scientist belief without evidence is gross professional misconduct. By turning a weakness into a strength the idea of faith squares the circle and smoothes down all the rough edges of any religion. Lenin tried to rid Russia of belief in God, but he kept blind faith in the motherland and the party instead.
Note, all those ideas were firmly in place in my head before I was old enough to use my own brain for myself. That is why Christianity, and similar well structured religions, have so much power over their believers. Before you confront the central point of whether or not you believe in God you have such a wealth of ammunition to prove to yourself that God must exist you don't really need to believe in any positive way at all.
Once you break that circle of self proof the Bible becomes just another book, written by many different people over a long time. For some reason it is no longer legitimate to add to the Bible, but obviously in biblical times, it was. Whoever gave legitimacy to the writers of the Bible is obviously no longer around. Christians say it is God who gives the Bible legitimacy... But that is a cheap debating point unworthy of me.