E1P19D
Demonstration — Part I
Latin
Deus enim (per definitionem 6) est substantia quæ (per propositionem 11) necessario existit hoc est (per propositionem 7) ad cujus naturam pertinet existere sive (quod idem est) ex cujus definitione sequitur ipsum existere adeoque (per definitionem 8) est æternus. Deinde per Dei attributa intelligendum est id quod (per definitionem 4) divinæ substantiæ essentiam exprimit hoc est id quod ad substantiam pertinet : id ipsum inquam ipsa attributa involvere debent. Atqui ad naturam substantiæ (ut jam ex propositione 7 demonstravi) pertinet æternitas. Ergo unumquodque attributorum æternitatem involvere debet adeoque omnia sunt æterna. Q.E.D.
English (Elwes 1883)
God (by Def. vi.) is substance, which (by Prop. xi.) necessarily exists, that is (by Prop. vii.) existence appertains to its nature, or (what is the same thing) follows from its definition; therefore, God is eternal (by Def. viii.). Further, by the attributes of God we must understand that which (by Def. iv.) expresses the essence of the divine substance--in other words, that which appertains to substance: that, I say, should be involved in the attributes of substance. Now eternity appertains to the nature of substance (as I have already shown in Prop. vii.); therefore, eternity must appertain to each of the attributes, and thus all are eternal. Q.E.D.
Modern English
God (E1D6) is substance, which necessarily exists (E1P11), that is, (E1P7), existence belongs to his nature, or (what comes to the same thing), it follows from his definition that he exists. So (E1D8) God is eternal.
Further, by God's attributes we must understand what expresses the essence of divine substance (E1D4), what belongs to substance. That is what the attributes themselves must involve. Now eternity belongs to the nature of substance, as I have already shown from (E1P7). Each attribute, then, must involve eternity, and so all of them are eternal. Q.E.D.