Early cultures developed belief systems to explain the unexplainable. Natural phenomena was explained through the belief in supernatural power (diety). These beliefs would connect (for example) the changes in the seasons or the rising and setting of the sun as an "act of god".
The same traditions continue today - through religious systems. These explain the 'purpose in life' and will answer all questions about the unknown (life after death, the rise and fall of governmental powers, global warming, etc.) by using 'ancient' writings.
"Life is without meaning. You bring the meaning to it. The meaning of life is whatever you ascribe it to be. Being alive is the meaning." -- Joseph Campbell