In my personal opinion, true free will necessitates the Divine. If one's fate is not ultimately determined by chemical reactions in her/his brain it seems as if humans must possess a nonphysical component, such as a soul/spirit/mind etc.
Therefore, it appears that we must look beyond the physical to the spiritual for the source of this component of our beings.
I "know" from my experience that part of my being, a non-physical component, is not controlled by chemical reactions.
It seems it would be difficult for one to reconcile this belief with disbelief in the Divine.
So this is how I see it: The Divine results in soul/spirit/mind, which is the only way "you" could ultimately be in control of your destiny.
How could one contend that chemical reactions are not responsible for his/her destiny without a belief in a non-physical component of humans? And if one believes in that non-physical component how can the Divine be denied?