Spinoza's Ethics: I.P24: Things Produced

This proposition, demonstration and corollary are fairly clear. I.D1 states "by cause of itself, I understand that whose essence involves existence, or that whose nature cannot be conceived except as existing." We then learn in I.D3 that only substance is conceived through itself and not through another, thus, substance is self-caused under I.D1. Then, in I.D6, we learn that God is a substance. Then in I.P14, we learn that, except God, no substance can be or can be conceived. All else is produced by God and all that which is not self-caused can be conceived as not existing. So, it would appear that when things involve existence, they are manifesting or expressing God immanently. The conceptual relationships of virtual to actual, energy to matter and potentia to Potestas are all useful in understanding the relationship of essence to existence.

Rerum a Deo productarum essentia non involvit existentiam.

Translated as,

The essence of things produced by God does not involve existence.

Demonstratio: Patet ex definitione 1. Id enim cujus natura (in se scilicet considerata) involvit existentiam, causa est sui et ex sola suae naturae necessitate existit.

Translated as,

This is evident from D1. For that whose nature (of course, considered in itself) involves existence, is the cause of itself and exists from the sole necessity of its own nature.

Corollarium: Hinc sequitur Deum non tantum esse causam ut res incipiant existere sed etiam in existendo perseverent sive (ut termino scholastico utar) Deum esse causam essendi rerum. Nam sive res existant sive non existant, quotiescunque ad earum essentiam attendimus, eandem nec existentiam nec durationem involvere comperimus adeoque earum essentia neque suae existentiae neque suae durationis potest esse causa sed tantum Deus ad cujus solam naturam pertinet existere (per corollarium I propositionis 14). 

Translated as,

From this it follows that God is not only the cause that things begin to exist, but also that they persevere in existing, or (so I might use a Scholastic term) God is the cause of the being of things. For whether the things exist or not, whenever we attend to essence of things, we learn that the same [essence] involves neither existence nor duration. So to such an extent the essence of things can be the cause neither of their existence nor of their duration but only God, to whose nature alone it pertains to exist (by P14C1).