You would notice a clear difference between someone ignorant of the concept of god, and people who are very familiar with the concept (like you) who have reached a decision to not believe in god. You cannot 'lack belief' in a concept that you understand. Familiarity with the concept 'god exists' requires you to accept this as true, or consciously reject the idea that it is definitely true. You don't lack belief on this you hold a belief.
For example:
"Is there a difference between believing and merely understanding an idea?Descartes thought so. He considered the acceptance and rejection of an idea to be alternative outcomes of an effortful assessment process that occurs subsequent to the automatic comprehension of that idea. This article examined Spinoza's alternative suggestion that (a) the acceptance of an idea is part of the automatic comprehension of that idea and (b) the rejection of an idea occurs subsequent to, and more effortfully than, its acceptance.
Spinoza argued that comprehending an idea did entail accepting that idea, however briefly. "Will and intellect are one and the same thing," he wrote, and thus, "I deny that a man makes no affirmation in so far as he has a perception" (1677/1982, pp. 97 and 99). Although Descartes's assumptions about the symmetry of acceptance and rejection and the disunity of comprehension and belief have silently dominated scientific thinking about these issues, psychological evidence suggests that Spinoza's hypotheses may have been closer to the truth. Findings from a multitude of research literatures converge on a single point: People are credulous creatures who find it very easy to believe and very difficult to doubt. In fact, believing is so easy, and perhaps so inevitable, that it may be more like involuntary comprehension than it is like rational assessment."
How Mental Systems Believe, Daniel T. Gilbert (February 1991 • American Psychologist)
