What does the old man mean by, "mysterious force" and how does he say it works?

I believe the mysterious force is a person's own mindset. When we work toward a goal that seems impossible to reach, we eventually hit a point where we give up on our dream. Melchizedek does not claim that the mysterious force is negative because it prepares a person's spirit and will so that he or she can understand "the one great truth on this planet."