In a world without God...

[Mister Agenda]

I can't believe the ruler of the universe would be behind a mind-game like this: I'll let you know I'm real if you believe in me, submit to me, and worship me based on what a bunch of Iron Age priests wrote down thousands of years ago.

Not a mind game. When someone of true power and authority in our soceity tells you to do XYZ if you want 123, then one does XYZ if He wants 123. Like If I was the little old lady who won that 600 million dollar power ball jackpot and I told you i will give you 100 million dollars if you washed my car with yellow joy liquid soap, rinsed it with bottled water and waxed it with liquid glass, would you wash and wax my car your way? Or would you do it per my instructions to make sure you got what I was offering?

If you would do this (bend your knee to me) for something as trivial as a 100 million dollars, then why would you expect to have God bend his knee before you to give you eternal life?

After all what does it profit a man if he were to loose his soul?

Argument from big stakes.

In your example, you're including in your assumptions that I'm aware that you have the money to pay me, which is the crucial difference between expecting someone to bend their knee to someone you claim exists and washing the car of a real person who really has 600 million dollars.

If a little old lady just told me she had 600 million dollars and would give me a 100 million for washing her car, I'd assume she was demented. I might still wash her car out of pity, not figuring I'll get anything for it.

Here's a better analogy: I'm walking down the sidewalk. You stop me and tell me if I wash this car in a driveway, the little old lady it belongs to has 600 million dollars and will give me 100 million dollars of her fortune.

I keep walking, maybe faster. Note that not only is the offer itself insane, even if the rich little old lady is real, it's insane to expect me to take your word for it or for me to lift a finger to find out if you're legit.