So far as we know, nature does not have a purpose. At least not any kind that humans would appreciate. Instead, nature seems to follow certain simple laws that are universal in scope such as Newton's laws of motion or the way that gravity decreases as the inverse square of distance. Matter and energy simply follow these laws blindly. Now, whether there is a true, genuine Purpose behind this entire arrangement, no one knows. Some say that God steers the whole thing, others say that purpose is just another kind of pattern that humans love to look for even in cases where it doesn't exist.