Personally, I've never had a belief in God, and tended to believe that the Abrahamic (why do people say 'Judeo-Christian' and exclude Islam?) concept of God and 'His' supposed purposes were incoherent. That doesn't mean that I didn't have a strong sense of 'spirituality', it just means that I didn't attach it to a concept of an anthropomorphic creator being. It was nature/existence itself that awed me.
Some Zen teachers occasionally talk in terms of 'God' - even the iconoclastic Brad Warner sometimes does. The word is being used as a way of expressing a Buddhist idea in 'Western' terms. However, the concept used here is far from the Abrahamic concept of a separate, self-existent, supernatural and (always to at least some extent) anthropomorphic creator used by most theists. Personally I tend to think that it should be avoided to avoid confusion.
There are some people - mainly Christian-Buddhist hybrids (not sure how that works) and Christians looking for common ground who try very hard to show that Buddhism and Christianity are essentially saying the same thing. I think that ultimately there may be an element of truth in this, but I think that a great deal of damage is done to a concept such as Sunyata (emptiness) by trying to squeeze it into a God-shaped hole. I tend to think that the concept of God is, in part, derived from experiences of 'no-self' and 'oneness', interpreted as a cosmic event - a union between a discreet self (individual soul) and a discreet Absolute (Godhead). This is naive and simplistic compared with the subtlety and sophistication of Nagarjuna's concept of Sunyata and Dogen's (and others') descriptions of the relationship between relative and absolute. In Buddhism, the denial of a separate self (anatman) and a separate absolute (nirvana) are key concepts. The rest as far as I can tell is a naive search for explanations which will fit into our common-sense conceptual structure on the basis of faulty logic and blind faith.
Even putting aside all the issues of evidence and the validity of 'personal revelation', and all the problems of Biblical literalism, I find the concept incoherent. Here is a small selection of the questions I think the idea of God begs:
Why would an omniscient, omnipotent, omnibenevolent being use methods of improving his creations, which required great suffering, (existence, freewill, evil, evolution) with no sign of resulting improvement?
Why would a perfect being need to create humanity let alone need its love?
Events/changes require time to occur in, so how could the creation of space-time occur before there was any time for it occur?
The usual answer to these sorts of questions is some variant of 'God works in mysterious ways', but this comes back to How do you know He works in mysterious ways?, How do you know the Bible is infallibly true?, How do you know that God exists?, How do you know (enough to make claims about it) what God is like?. Blind faith - a personal feeling of conviction isn't valid, as demonstrated by the number of people who have absolute faith in their beliefs and yet who contradict each other or who are demonstrably false and/or insane. Faith in Buddhist practice, as I understand it, is of a more ordinary sort - like the faith of a climber in his ropes. The 'intuitive knowing' described about 'enlightened masters' is something else - 'knowing' is not quite the right word and it is not knowledge of anything supernatural or metaphysical - rather, it is just being fully attentive to reality, absent of certain illusions we have about it.
I find it interesting that the less literal the interpretation of Biblical and traditional explanations of God are - the more 'ineffable' they are, the less problematic they become, because such claims are less concrete. Instead of the jealous tribal god Yahweh who lives on Mount Sinai and smites the enemies of Israel, God becomes a cosmic source or principle beyond space and time, almost equivalent to the deepest laws of physics. A consequence of this is that the more anthropomorphic supposed 'purposes' of this entity start to become absurd. 'God is the unknowable source, the will of nature, the very ground of all being...and He hates gays.'
If God is a synonym for the deepest principles of physics, what word is left for a hypothetical being who answers prayers, intervenes to save cancer patients or helps evolution over difficult jumps, forgives sins or dies for them?Richard Dawkins
I came across this excerpt and really enjoyed it. I know that 'Zen talk' can seem pretty bizzare so I've added my interpretations of what Seung Sahn said.
After one of the Dharma Teachers was finished with his introductory remarks, he asked those congregated to direct their questions to Zen Master Seung Sahn, Soen Sa Nim. One of the visitors asked if there was a God.
Soen Sa answered "If you think God, you have God, if you do not think God, you do not have God."
[God and the absence of God are mental constructs]
"I think that there is no God. Why do I have God if I think God?"
"Do you understand God?"
"No, I don't know."
"Do you understand yourself?"
"I don't know."
"You do not understand God. You do not understand yourself. How would you even know if there was a God or not?"
"Then, is there a God?"
"God is not God, no God is God."
[Apart from our mental contruction there is inherently no God or absence of God. Alternatively - the Ultimate (God) and nothingness/absence of inherent nature/interdependence are the same. ]
"Why is God not God?"
Holding up the Zen stick, Soen Sa said "This is a stick, but it is not a stick. Originally, there is no stick. It is the same with God for originally there is no God. God is only name. The same is true of all things in the universe."
[Conventionally sticks exist, but ultimately they do not, for their nature is dependent. The same is true for God.]
"Then is there no God?"
"The philosopher Descartes said, 'I think therefore I am.' If you do not think, you are not, and so the universe and you are one. This is your substance, the universe's substance, and God's substance. It has no name and no form. You are God, God is you. This is the 'big I,' this is the path, this is the truth. Do you now understand God?"
[All things (including 'God' and 'no God') are ultimately of one substance. Is this God? It cannot be named.]
"Yes, I think that there is no God, and I have no God."
"If you say that you have no God, I will hit you thirty times. If you say that you do, I will still hit you thirty times."
[By saying there is or there is not a God, the visitor is trapped by thought and language and unable to apprehend reality as it is before conceptual thought distorts it. Reality is not found at either of these extremes but in a non-conceptual 'Middle Road' between them. The threat of violence is just gentle encouragement.]
"Why will you hit me? I don't understand. Please explain."
"I do not give acupuncture to a dead cow. Today is Tuesday." replied Soen Sa.
[This is a waste of time. Forget all that abstract stuff - this is reality].
I just found this short little piece, which I also like:
Zen Master (to student): Do you know God?
Student: I don't know
ZM, Do you know Buddha?
Stu, I don't know
ZM, Do you hear the waterfall?
ZM, Just That.
[Forget your ideas about God or Buddha - the sound of the waterfall is the real 'God'/'Buddha' ie. ultimate reality, not some idea about something transcendent but reality itself]