Kant 2nd Part, Sec 17

"The formal aspect of nature in this narrower sense is therefore the conformity to law of all the objects of experience, and so far as it is known a priori, their necessary conformity. But it has just been shown that the laws of nature can never be known a priori in objects so far as they are considered not in reference to possible experience, but as things in themselves. And our inquiry here extends not to things in themselves (the properties of which we pass by), but to things as objects of possible experience, and the complex of these is what we properly call nature"

Before I begin to even detail the passage, I just wanted to note that this is by far the most challenging piece of writing I have ever read to understand. In fact, Kant's whole book was difficult.

In this this passage, Kant explains how nature's law of conformity relates to not just expierencing them but them just being themselves. The human mind inquires about them even without the expierence. This is what defines nature. Its something that can't really be changed but is all around us and we want to find out more about it.