Spinoza's Ethics: I.P34: God's Power

The Latin word potentia is used here for power. This word is significantly different than another Latin word that Spinoza uses for power which is potestas. Potentia is closely connected with the English cognate of "potential" as potentia signifies the expressive and dynamic notion of power as the virtual becomes actual. Potestas signifies an inertial force to maintain an order. Within Spinoza's framework, potestas always gives way to potentia.

Dei potentia est ipsa ipsius essentia. 

Translated as,

The power of God is [God's] essence itself.

Demonstratio: Ex sola enim necessitate Dei essentiae sequitur Deum esse causam sui (per propositionem 11) et (per propositionem 16 ejusque corollarium) omnium rerum. Ergo potentia Dei qua ipse et omnia sunt et agunt, est ipsa ipsius essentia. Q.E.D.

Translated as,

For from the only the necessity of the essence of God, it follows that God is the cause of itself (by P11) and (by P16 and P16C) of all things. Therefore, the power of God, by which God all things are and act, is [God's] essence itself.