When you use 'God' it means it is just one defined being,that therefore doesn't need an indefinite article because it is a definite one, nor a definite article to differentiate between it and others,because it is only one .This usage reflects the belief in one God , in other words 'monotheism'. In monotheistic religions like Christianity and Islam ,you will find the word 'God' used without article in most cases specially in prayers ! However you could hear "The God will punish you". It is not commonly used this way though. While when believing in more than one God, what is called Polytheism, 'the God' is more often used to refer to one specific God of many Gods. In greek mythology where there exist many Gods, you will notice the reference to God as 'The God'. "He was the God of wealth."

it is depens on that topic you are talking about. if you talking "god" in hindu, they are many gods, so, it have to be specified which gods you are refering. but if you talking with a muslim or christian, they know who you refering too. for sum up. wethers god or the god. it is the same. it rather depends on who you are communicating with.

First of all, you can't be lazy in capitalizing the word "God". In English, it means the God of Abraham, ie Yahweh, the highest being in Christianity etc. Without capitals it means gods from other places. However the meaning of "the God" varies in the context. For example, "the God of War". In language context, "the God" means a particular god where as having just god can mean any god. Of course to fanatics of any monotheistic religion, this would be sacrilegious and insulting. Then other cultures refused to have the word god. For example, in Islam, God is Allah and this will differentiate what one is referring to. To the Chinese, the word Heaven is synonymous with God.