What can and cannot exist is set by the nature of the primary particles and the limited ways in which they articulate. Ultimate control is by these relatively simple mechanisms. There is no purpose in nature, as such, other than to do what it is and be what it can be. Until the development of intelligent life, existence is purely mechanistic. With the development of a conscious and reasoning brain, planning and purpose enter into the equation.
Intelligent life is the universe gaining self-awareness.
As consciousness emerges, learning and reasoned determinations enter the picture, increasing as the intelligence increases. It is only then that purpose enters the picture, the determinations of a naturally autonomous individual life form. The purpose of one's life is no more, and no less, than the individual gives the self, although the autonomy of an individual can be usurped by others, or volitionally given. In such case this individual becomes the tool of another, and takes on the purpose of someone or something else. This work in physics by R. Srewart Hall has relevance for all human thought, and implications for every field of inquiry.