I don't understand the necessity of this distinction - why would I feel compelled to force the concept of divinity into some linguistic compacting such as "a God"? Why can't I believe in many Gods? Or maybe Many Gods underneath a supreme, whole "one" God? If the latter, then why talk about just "a God" ? That makes no sense to me.
Do you wanna know what I believe? I believe that if I believe in God, and if I believe that the descriptions of God that are given to me as such ARE TRUE, there's more than "one God" - or at least, there are "spheres" of God that we can describe as being MULTIPLE. Hence we need more than A God.
If i'm not mistaken, Christianity does just this!!

You don't need "a God", you need many and you need them badly.
Besides, why would I believe in A God when I can believe in ALL GODS?!? The latter is much more amusing, trust me

Ever see Zeus play a prank on St Peter? I have. It was pretty violent for a prank, but it got laughs from the onlooking angels.