P20: God/Nature’s existence and his essence are one and the same.

Dem.: God/Nature (by P19) and all of his attributes are eternal, i.e. (by D8), each of his attributes expresses existence. Therefore, the same attributes of God/Nature which (by D4) explain God/Nature’s eternal essence at the same time explain his eternal existence, i.e., that itself which constitutes God/Nature’s essence at the same time constitutes his existence. So his existence and his essence are one and the same, q.e.d.

Cor. 1: From this it follows, first, that God/Nature’s existence, like his essence, is an eternal truth.

Cor. 2: It follows, secondly, that God/Nature, or all of God/Nature’s attributes, are immutable. For if they changed as to their existence, they would also (by P20) change as to their essence, i.e. (as is known through itself), from being true become false, which is absurd.