On August 2, 2006, Elon Musk wrote the first Tesla blog post titled “The Secret Tesla Motors Master Plan (just between you and me).” In that post Musk clearly explained his strategic plan for Tesla.
He starts off by explaining the story behind Tesla, or the why.
The overarching purpose of Tesla Motors (and the reason I am funding the company) is to help expedite the move from a mine-and-burn hydrocarbon economy towards a solar electric economy, which I believe to be the primary, but not exclusive, sustainable solution. – Elon Musk