I write from a Western “Christian” background having studied the history of belief and specifically the Church’s belief system from the perspective of an intrigued amateur for many years.  My thoughts only extend to the Western mind. I will leave it to others if they wish to extend or alter the arguments to other cultural mind sets.

I will briefly examine the various arguments for the existence of God

Ontological Argument
Briefly stated this argument goes. God is defined as being the most perfect being. Of all the beings in the universe, one must be the most perfect beyond all others. This is God. God exists. This is nonsense – all we have done is to say that the most perfect being exists – that’s not God in any meaningful sense. 
It is difficult to understand why a trivial argument should be trotted out in all the textbooks or why the serious study should have been devoted to it in the Middle Ages – except that it is possible to embellish the argument and express it in many more convoluted ways.

First Cause Argument
The universe had a first cause. Let’s call that God. That’s the argument. Not very convincing is it?

Design Argument
The most persuasive argument, for me, for the existence of God is the design argument. The argument goes along the lines that if you were walking along a beach and saw a watch without knowing anything else you could deduce that it was produced by an intelligence. The universe is so cleverly put together that this must imply an intelligent creator- that is God.

There are arguments against this. For example – this universe is designed the way it is because this is the only design that works, or we just happen to live in this universe as opposed to any number of parallel universes and because we know of no other we think of it as uniquely desirable. If the universe had to be created by God didn’t God have to be created?

One aspect of this argument that I haven’t seen anywhere else is that the design of the universe to at once obey physical laws but simultaneously be non deterministic is pretty clever stuff. It is so clever that maybe we can infer an intelligence at work.

God Provides the Simplest Explanation Argument
If you believe in God you might have all the answers you need neatly packaged. I have argued previously that you are free to believe this. Belief might give you the universal answer to everything. Occam’s Razor is often paraphrased as “all things being equal the simplest explanation is the best”. If one accepts this then it is a powerful argument for the existence of God since it provides the ultimate explanation for everything. 

God is Unknowable
The human brain cannot conceive of the infinite. God is omniscient and omnipresent, by definition, and it is impossible to have any understanding of such a being. To try is pure folly. Therefore believe and he will help your unbelief. I’ve tried this and it didn’t work for me.

We are now prejudiced 
It was the simple belief – God explains everything- that persisted for some 2000 years in various guises that held the “progress of man” back. It is difficult to put our minds back to that thought process. It was generally believed that if you had a disease you would die if God willed it or live if He wished. Simple.  If you were in a battle you would win or live if God willed it and if not – then that was that. Guilt or otherwise at a trial could be determined by the outcome of a test in which God would intervene (trial by ordeal). I am sure that there were many cynics throughout time but this prevailing ethos did hold.

So we had a near universal public belief in God. It was very useful in many respects, it was very reassuring to believe in a father figure and life after death was very palatable. If it seems that we cannot prove or disprove the existence of God then it is sensible to believe since that way we win if he does exist and if he doesn’t we have only wasted a small amount of time. It can be argued that we are now so prejudiced by science that we cannot see this simple truth. 

What About Divine Revelation?
It is noticeable that in all of the discussions of the existence of God, it is rare that anyone discusses their attitude to divine revelation either through the Christ or miracles. One interesting point that has been made is that as the Bible progresses references to God diminish in frequency until he has all but disappeared.

The fact is that I don’t think the church needed the Christ at all. Arguably the Church really only came into being when the Roman Emperor Constantine wanted to consolidate his power. Christianity just happened to be the creed he could use. The Church became the long echo of the Empire and altered the Christian value set beyond recognition. Divine revelation was out and power politics was in. I know this is a crude oversimplification and there have been a lot of devout people around but the facts are largely as stated. So if the Church very rapidly gave up on a creed based on the initial divine revelation and went on to get itself tied up in the nature of the Trinity and the date of Easter. I think it is reasonable therefore as people seem to, to leave the Church outside the argument.

What about Miracles?
Given that the human body and mind are non deterministic it would be strange if it did not observe and behave in ways that are inexplicable. I see no particular reason why this should then allow a leap to the existence of God.  

Could God Intervene?
How can we trust in God if we don’t believe in His intervention? On the other hand, if we do believe in His intervention how can we believe in science, because a basic postulate of science is that given the same set of circumstances, the same thing will happen (scientific determinism). This postulate has seemed remarkably robust. It has been very useful, but I believe that it is wrong. Science to make progress has been forced to seek out deterministic processes and some how we ended up believing that we only had to look hard enough and everything would be explained by science. This is simply not so.  The universe and our world is non deterministic.

Does God Matter? 
If God exists then he will have an agenda that we cannot know or understand. He clearly doesn’t intervene as a daily occurrence as he seemed to do in the old testament. I cannot comprehend the idea of a supreme being requiring human kind to prostrate themselves before him and worship him. 

Does the idea of God provide a moral framework for us to live our lives?
Yes, it does but then we can derive this easily without.

Is the idea of God tied up with the idea of an after life?
Yes and I think here is where it becomes important.