If you fundamentally believe that God determines all then the concept is free will does not apply to you.
I think that is what Rembrandt is getting at.
So a God fearing person would choose the box in which God indicated he would put one million because God know what you are thinking. If you opened the second box and there have nothing in it then he works in mysterious ways and this was his will If you don’t believe God knows what you are thinking you would take both and hope he put the million in the second one. By looking for the answer one conclusion would be that you are not sure if God knows what you are thinking.
