I think that since the beginning of time our purpose on earth was to figure out what compelled us towards the heavens. All the civilzations since the beginning have been willing to die and spend massive amounts of time and back break labor to build temples and tombs to prepare themselves for the next lifetime. All religions for the most part agree in one ultimate God over all the others.
So, I beleive that if you're a spiritual/logical person who believes in the notion that everyone has a soul... it is logical to think that our ultimate purpose is to praise God! 