You can believe that some object fails to possess some property for reasons other than a lack of evidence. For example, I believe there are no integers greater than three but less than two. This is not merely because I've never encountered such a number, but because the integers are defined such that I can believe with unfailing certainty that I never will. Anything that might be both greater than three and less than two is by definition not an integer.

Similarly, any conception of God worth taking seriously to begin with is not simply any arbitrary vector in the space of all possible properties. The orientation of the "god vector" along any given axis should satisfy at the very least some aesthetic criterion - and if possible some logical one - which accords with a rank ordering of all positions by some definition of "greatness". Without a metric of greatness by which to specify the location, or range of locations, of a conceptual vector along dimensions of interest, there is no concept whatever left to be analyzed.

If it is given that such a metric is a necessary element in a obtaining a robust, non-arbitrary conception of God, it follows that the same rules emphatically do not apply to both essential and inessential properties. Some properties can be rejected out hand merely because they violate the rank-ordering necessary to identify the concept in question.

Moreover - essential properties may not be asserted to not belong to at least one object without simultaneously denying the existence of that object (since any object satisfying the spanning set of some concept's defining properties is an instantiation of it), whereas inessential properties may be regarded as either applying to the object or not without compelling us to adopt any particular propositional attitude towards its existence.