Everything operates by the fundamental law of cause and effect, which is upheld by Newton's 3rd Law. This means that even your synapses in your brain fire because of things that made them fire. We don't have free will scientifically speaking. The thing that looks like free will is programming through cause and effect. This is scientific law.
You making an assumption that consciousness is a product of brain function, that has not been proved. This is why there is no unit of measure for consciousness. Some argue that our brains are merely receivers of consciousness like a biological TV set. Hence free will is not necessarily a product of cause and effect. Your free will could very well be influencing/driving the synapses in your brain that fire.
Assuming you support the idea of religion, arguing that your consciousness is merely a product of the brain due to cause and effect, implies we are biological robots. Then what purpose would religion even have.