P18: God/Nature is the immanent, not the transitive, cause of all things.

Dem.: Everything that is, is in God/Nature, and must be conceived through God/Nature (by P15), and so (by P16 C1) God/Nature is the cause of {all} things, which are in him. That is the first {thing to be proven}. And then outside God/Nature there can be no substance (by P14), i.e. (by D3), thing which is in itself outside God/Nature. That was the second. God/Nature, therefore, is the immanent, not the transitive cause of all things, q.e.d.