First off, to all the ignorant who do mock the "G-d" spelling, it is because they do not wish to use His name in vain. They take His name as sacred and not to be used in commonplace conversation.
Anyways, I do not think any of us have that answer. The Jewish G'd (Hashem) is meant to be worshipped and obeyed. He is greater than we can comprehend, so for as common as this question of purpose is, the only thing known is that 1) Yah is sovereign, 2) We are man. 3) Man was made to worship G-d. 4) Yah has displayed his love and mercy on mankind.