God or god?

"...regarding ‘God’ as the proper name of the Deity, rather than as essentially a common noun, implies that all users of the word are monotheists and, within that, that all monotheists believe in the same god. Both these propositions seem to me self-evidently untrue. It may or may not be true that any worship of any god is translated by some mysterious grace into worship of one god who actually exists, and who happens to be the only god. That is believed by some students of religion. It is not, however, believed by very many practitioners of the mainline monotheistic religions (Judaism, Christianity, Islam) or of the non-monotheistic ones (Hinduism, Buddhism and their cognates). Certainly the Jews and Christians of the first century did not believe it." - Volume One
The New Testament: And The People Of God. N.T. Wright (p. XV).