hashkafah philosophy - Why is being religious a duty if God chose to not have a proof to his existence in this world?

According to the answers to the question "How do we know that God exists" it seems some (if not most) Jews on this site believe there is no way to verify whether or not God even exists.

If this view is correct, how can God expect people to view religious service as a duty and be subject to punishment in the afterlife for failing to live up to it.

After all, there is no way to even know whether He even exists. Are we expected to be religious out of doubt? How could God expect us to devote ourselves 100% to Him (pray to Him, trust in Him, give up our lives for Him if needed, etc.) if we cannot be sure He even exists?

(note that I personally totally disagree with this view, but I am asking according to it.)

I am not asking for proofs of God or Judaism.