I think that purpose is something created by us, unless you believe that all humans are predestined to something, but in that case there would be no free will.
There is only the illusion of free will. After all, the synapses that fire are caused to fire by certain biochemical actions that are in the brain. The result is that we feel that there is free will. But we don't understand, scientifically, how there can be any. Science doesn't have the answer for the existence of free will.
Note that I believe we have a tiny bit of free will. It isn't in the feelings we have when we seem to make free choices. That isn't free will. The free will lies in us in some other way.
