The main feature that differentiates these two prepositions "por" and "para" is that the preposition "para" express aim or purpose, and answers the question "for what? or for whom?". On the other hand the preposition "por" express cause and respond to the question "why?"

http://www.pyc-revista.com/numAnt/num4/15_gramatica.pdf http://www.phrasebase.com/archive/spanish2/por-vs-para.html Of course "por" "para" are not the same....