If this be denied, then God is not the cause of the essence of things; and therefore the essence of things can (by Ax. iv.) be conceived without God. This (by Prop. xv.) is absurd. Therefore, God is the cause of the essence of things. Q.E.D.
Modern English
Suppose God is not the cause of the essence of things. Then (E1A4) the essence of things can be conceived without God. But that is absurd (E1P15). Therefore God is the cause of the essence of things as well. Q.E.D.