Athiest, what is a soul? Do you have a soul? Do you have an immortal soul? What makes a soul immortal?
You can answer all of these questions without any theology, no mention of god, no world religious views, just use your intellect and reason. Use philosophy and meta-physics, both non-religious in any way and I suspect that would be your first step in seeking the Truth. (Hint: think ancient Greek philosophers, Socrates, Aristotle, and Plato)
And, as analogies go, no analogy can ever be comprehensive as they only connect on very small aspects of detail. Without having to get to my 3,200 word limit per post … the marble thing didn’t make sense to me as the points of contact between the existence of god and the differentiation between the determination of an even or odd number of physical and contained objects just didn’t make sense to me.
Then, there is always the concept of non-contradiction. Put your cell phone in your hand, does it exist? It either has to exist or does not exist, there is no “well, I’m not sure, it might be in existence or it might not”. Thus, in the exact same concept, God either exists or does not exist, there can be no other state. Thus, if an atheist position is that “God does not exist” … then as the atheist pushes the burden of proof on the theist, “prove to me God exists” … by the very same measure, I would ask the atheist, “prove to me that God does not exist.” and the we’re off to the races!