Let us accept for the moment that the soul exists. Scientists haven’t evidenced this, thus far. One tried to weigh the soul and determined its weight at 21 gms. Scientists debunked the test as an experiment without sufficient rigor. In the absence of evidence, let us momentarily rely on scriptures. Next, let us examine belief. Scientists have posited that belief occurs in several areas of the brain. The frontal lobes, of the cortex, unique to humans or the more evolutionary and ancient regions deep inside the brain. The exact location is debated. However, it is not argued that thought, reason, and belief occur in the brain. Finally, we act. Our actions may be consistent with our beliefs. Often, we act to the contrary. Arjun in the Mahabharata for example. It required God to appear before Arjun could suspend his beliefs for a perceived positive outcome. I now beg to leave to make the argument that action, belief, and the soul are three separate planes. How they interact is an intriguing question.
Does the soul determine belief and action? I suppose not, since the soul has not shown itself to have natural senses. Where then does the debate between one version of your belief and another take place? Certainly not in the soul? If not then clearly action cannot be determined by the soul either. Action, after all, is merely the manifestation of your beliefs in physical form. Slapping someone you are angry with, for example. Your belief determined you were entitled. Your hands complied. Your soul did not have much say did it?
In such a construct what therefore may be a role for the soul? Imagine the soul as a bookkeeper. It monitors long term; across multiple lifetimes. It keeps a record of your thoughts, choices, beliefs and actions. Itself, it remains unchanged. There is no instrumentality to change it, is there?