De Deo uno
The first cause is not yet fully understood until its necessary attributes are drawn out
If the first cause contained passive potency, it would require an actualizer and would not be first. It is therefore pure act. If it were composed of parts, act and potency, essence and existence, substance and accident, or genus and difference, the composition would require a cause of unity and actuality. It is therefore simple. What is simple and without potency cannot acquire or lose actuality; it is immutable.
Time measures change according to before and after. An immutable first cause is not spread through temporal succession and is therefore eternal, possessing life without beginning, end or intrinsic change. Immateriality follows because matter is a principle of potency and individuation within material species. Unity follows because two pure acts could not differ by a perfection one possesses and the other lacks without introducing potency and limitation.
Perfection belongs to the first cause because every actuality found in effects must be present in the cause either formally or eminently, without creaturely limitation. Intelligence is required because the universal order of forms and ends cannot arise ultimately from blind derivative powers. Goodness belongs because being and goodness are convertible, and the first cause is the unreceived fullness of actuality.
These conclusions must remain analogical. Divine knowledge is not a process of learning; divine will is not a change from indecision; divine power is not a capacity awaiting activation. Creation adds no perfection to God and imposes no necessity upon Him. The finite world depends wholly upon God, while God does not depend upon the world. This asymmetry is the heart of classical theism and distinguishes it from pantheism, deism conceived as a remote engineer, and mythological gods within the cosmos.
Reader path: Summa Theologiae I, q. 3-26 · Lateran IV and Vatican I
